As filed with the Securities and Exchange Commission on February 6, 2025

Registration No. 333-283805

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UNITED STATES SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

PRE-EFFECTIVE AMENDMENT NO. 1 TO THE

FORM S-1

REGISTRATION STATEMENT UNDER THE

SECURITIES ACT OF 1933

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Marathon Bancorp, Inc. and

Marathon Bank 401(k) Plan

(Exact Name of Registrant as Specified in Its Charter)

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500 Scott Street

Wausau, Wisconsin 54403

(715) 845-7331

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

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Nicholas W. Zillges

President and Chief Executive Officer

500 Scott Street

Wausau, Wisconsin 54403

(715) 845-7331

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

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Copies to:

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Approximate date of commencement of proposed sale to the public: As soon as practicable after this registration statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box: ☒

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If this Form is filed to register additional shares for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering: ☐

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If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering: ☐

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If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering: ☐

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Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.:

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If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided to Section 7(a)(2)(B) of the Securities Act. ☐

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The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

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Prospectus Supplement

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MARATHON BANK 401(k) PLAN

Offering of Participation Interests in up to 427,710 Shares

of

MARATHON BANCORP, INC.

Common Stock

Marathon Bancorp, Inc., a Maryland corporation that we refer to as “Marathon Bancorp” throughout this prospectus supplement, is offering shares of common stock for sale at $10.00 per share in connection with the conversion of Marathon MHC, which we refer to as the “MHC” throughout this prospectus supplement, from the mutual holding company to the stock holding company form of organization. The shares being offered represent the ownership interest in Marathon Bancorp, for which the MHC currently owns more than 50% of the outstanding shares. Marathon Bancorp’s common stock currently trades on the Pink Open Market, operated by OTC Markets Group under the trading symbol “MBBC.” Following the offering, we expect Marathon Bancorp’s common stock will trade on the NASDAQ Capital Market also under the trading symbol “MBBC.” We must sell a minimum of 1,402,142 shares to complete the offering.

In connection with the stock offering, Marathon Bank is allowing participants in the Marathon Bank 401(k) Plan (the “401(k) Plan”) to invest all or a portion of their account balances in Marathon Bancorp common stock. Based upon the value of the 401(k) Plan assets at December 31, 2023, the trustee of the 401(k) Plan could purchase up to 427,710 shares of Marathon Bancorp common stock, at the purchase price of $10.00 per share, in the stock offering. This prospectus supplement relates to the election of 401(k) Plan participants to direct the trustee of the 401(k) Plan to invest all or a portion of their 401(k) Plan account balances in Marathon Bancorp common stock at the time of the stock offering.

Before you consider investing, you should read the prospectus of Marathon Bancorp, dated [prospectus date], which is attached to this prospectus supplement. It contains detailed information regarding the conversion, the stock offering of Marathon Bancorp and the financial condition, results of operations and business of Marathon Bank. This prospectus supplement provides information regarding the 401(k) Plan. You should read this prospectus supplement together with the prospectus and keep both for future reference.

For a discussion of risks that you should consider, see “Risk Factors” beginning on page 1 in this prospectus supplement, “Risk Factors” beginning on page 16 of the attached prospectus, and “Notice of Your Rights Concerning Employer Securities” in this prospectus supplement.

The interests in the 401(k) Plan and the offering of the shares of Marathon Bancorp common stock have not been approved or disapproved by the Federal Deposit Insurance Corporation, the Board of Governors of the Federal Reserve System, the Wisconsin Department of Financial Institutions, the Securities and Exchange Commission or any other federal or state agency. Any representation to the contrary is a criminal offense.

The securities offered by this prospectus supplement are not deposits or savings accounts and are not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.

This prospectus supplement may be used only in connection with offers and sales by Marathon Bancorp in the stock offering of Marathon Bancorp common stock that may be acquired within the 401(k) Plan. No one may use this prospectus supplement to reoffer or resell interests in shares of Marathon Bancorp common stock acquired through the 401(k) Plan.

You should rely only on the information contained in this prospectus supplement and the attached prospectus. Marathon Bancorp, Marathon Bank, and the 401(k) Plan have not authorized anyone to provide you with different information.

This prospectus supplement does not constitute an offer to sell or solicitation of an offer to buy any securities in any jurisdiction to any person to whom it is unlawful to make an offer or solicitation in that jurisdiction. Neither the delivery of this prospectus supplement and the attached prospectus nor any sale of Marathon Bancorp common stock shall under any circumstances imply that there has been no change in the affairs of Marathon Bancorp, Marathon Bank or the 401(k) Plan since the date of this prospectus supplement, or that the information contained in this prospectus supplement or incorporated by reference is correct as of any time after the date of this prospectus supplement.

The date of this prospectus supplement is ____________, 2025.

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TABLE OF CONTENTS

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RISK FACTORS

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In addition to considering the material risks disclosed under “Risk Factors” beginning on page 16 of the attached prospectus, you should also consider the following:

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If you elect to purchase Marathon Bancorp common stock using your 401(k) Plan account balance and the stock offering is oversubscribed, you will bear the risk of price changes in the investment funds of the 401(k) Plan.

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If you elect to purchase Marathon Bancorp common stock using your 401(k) Plan account balance, the 401(k) Plan trustee will sell the designated dollar amount within your 401(k) Plan account pro rata among your investment fund balances (other than the existing Marathon Bancorp Stock Fund). If the stock offering is oversubscribed (i.e., there are more orders for Marathon Bancorp common stock than shares available for sale in the stock offering) and the 401(k) Plan trustee cannot use any or all of the funds you allocate to purchase Marathon Bancorp common stock in the stock offering, the funds that cannot be invested in Marathon Bancorp common stock, and any interest earned on those funds, will be reinvested in your existing investment funds of the 401(k) Plan (other than the existing Marathon Bancorp Stock Fund), according to your then existing investment elections (i.e., in the same proportion as your investment direction for future contributions). During the period from when the 401(k) Plan trustee sells a percentage of each of your investment funds until reinvestment of some or all of those funds back into your investment funds as a result of an oversubscription, you will bear the risk of price changes in the investment funds. It is possible that during this period some or all of the investment funds may have increased in value more than the amount of any interest you may have earned on the reinvested funds before reinvestment. See “The Offering – Purchases in the Stock Offering and Oversubscriptions” in this prospectus supplement.

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THE OFFERING

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DESCRIPTION OF THE 401(k) PLAN

Introduction

Marathon Bank originally adopted the predecessor plan to the 401(k) Plan effective as of January 1, 1996. The 401(k) Plan is a single-employer, tax-qualified plan with a cash or deferred compensation feature established in accordance with the requirements under Section 401(a) and Section 401(k) of the Internal Revenue Code of 1986, as amended (the “Code”).

Marathon Bank intends that the 401(k) Plan, in operation, will comply with the requirements under Section 401(a) and Section 401(k) of the Code. Marathon Bank will adopt any amendments to the 401(k) Plan that may be necessary to ensure the continuing qualified status of the 401(k) Plan under the Code and applicable Treasury Regulations.

Employee Retirement Income Security Act of 1974, as amended. The 401(k) Plan is an “individual account plan” other than a “money purchase pension plan” within the meaning of ERISA. As such, the 401(k) Plan is subject to all of the provisions of Title I (Protection of Employee Benefit Rights) and Title II (Amendments to the Code Relating to Retirement Plans) of ERISA, except to the funding requirements contained in Part 3 of Title I of ERISA, which by their terms do not apply to an individual account plan (other than a money purchase plan). The 401(k) Plan is not subject to Title IV (Plan Termination Insurance) of ERISA. The funding requirements contained in Title IV of ERISA are not applicable to participants or beneficiaries under the 401(k) Plan.

Reference to Full Text of 401(k) Plan. The following portions of this prospectus supplement summarize certain provisions of the 401(k) Plan. They are not complete and are qualified in their entirety by the full text of the Marathon Bank 401(k) Plan. Copies of the 401(k) Plan are available to all employees by filing a request with the 401(k) Plan Administrator c/o Marathon Bank, Attn: Joy C. Selting-Buchberger, Senior Vice President and Chief Financial Officer. You are urged to carefully read the full text of the 401(k) Plan.

Eligibility and Participation

As an employee of Marathon Bank, you are eligible to become a participant in the 401(k) Plan for purposes of making elective deferrals on the entry date coinciding with or immediately following your attainment of age 19. The entry dates under the 401(k) Plan are the first day of each calendar quarter.

As of December 31, 2023, there were approximately 51 active and former employees in the 401(k) Plan.

Contributions under the 401(k) Plan

Employee Elective Deferrals. 401(k) Plan participants are permitted to defer any whole percentage of their Compensation (as defined below) from 1% to 100% of their Compensation, subject to certain restrictions imposed by the Code, and to have that amount contributed to the 401(k) Plan on their behalf. Participants may make either traditional 401(k) deferrals (pre-tax) or Roth deferrals (after-tax with potential tax-free growth). Your pre-tax deferrals are not subject to income tax until distributed from the Plan. Roth deferrals are subject to income tax at the time of the deferral but are not taxed when distributed from the Plan if certain eligibility requirements are met (i.e., allowing for tax-free growth). For purposes of the 401(k) Plan, “Compensation” means Form W-2 wages, including compensation due to SEP deferrals (under Section 402(h)(1)(B)), cafeteria plan deferrals (under Section 125), deemed Section 125 compensation, transportation compensation (under Section 132(f)(4)), Sections 401(k) and 403(b) deferrals, Section 457(f) deferrals, and 402(k) deferrals. For 2025, the Compensation of each participant taken into account under the 401(k) Plan is limited to $350,000, and participants may generally defer up to $23,500 and may defer an additional $7,500 if they qualify for catch-up contributions (limits established by the Internal Revenue Service are subject to increase pursuant to an annual cost-of-living adjustment, as permitted by the Code). Canceling or changing a deferral contribution percentage can be accomplished by contacting Human Resources.

Roth Elective Deferrals. You may elect to designate all or a portion of deferrals as Roth elective deferrals. Roth elective deferrals do not reduce your total taxable income or your current taxes. Because you pay taxes on these contributions when they are made, these contributions will not be taxed later when received as a benefit and distributed as a qualified distribution. A distribution will be a qualified distribution if (i) the distribution is made on or after you attain age 59 ½, on or after the date of your death, or as a result of you becoming disabled as defined by the Code; or (ii) the distribution is made after the end of the 5-taxable year period beginning with the first taxable year in which you make a Roth elective deferral contribution to this plan.

Catch-up Contributions. Participants who have made the maximum amount of regular before-tax contributions allowed by the 401(k) Plan or other legal limits and have attained at least age 50 (or will reach age 50 before the end of the Plan Year, which is December 31), are also eligible to make an additional catch-up contribution. For 2025, the maximum catch-up contribution is $7,500. Participants may authorize Marathon Bank to withhold a specified dollar amount of their Compensation for this purpose.

Employer Matching Contributions. Marathon Bank currently makes a Matching Contribution equal to 50% of a participant’s pre-tax elective and Roth elective deferrals and catch-up contributions, up to 6% of a participant’s Compensation, for a maximum matching contribution of 3% of participant Compensation.

Employer Profit Sharing Contributions. Marathon Bank may make a profit-sharing contribution to the Plan each year and in such amount, if any, as it may determine. To be eligible to receive an allocation of the discretionary employer profit sharing contribution, you must complete 1,000 hours of service during the Plan year and be employed the last day of the year.

Employer Safe Harbor Contributions. The 401(k) Plan takes advantage of certain rules that provide alternative methods to pass the non-discrimination tests required of 401(k) plans. Under these rules, the Marathon Bank has elected to provide a contribution to all employees eligible to make salary deferrals. The safe harbor contribution will be made as a safe harbor non-elective contribution in the amount of 3% of each eligible participant's compensation.

Limitations on Contributions

Contribution Limits. For the Plan Year beginning January 1, 2025, the amount of before-tax contributions may not exceed $23,500 per calendar year, or $31,000, if a participant is eligible to make catch-up contributions. Contributions in excess of this limit are known as excess deferrals. For participants who defer amounts in excess of this limitation, their gross income for federal income tax purposes will include the excess in the year of the deferral. In addition, unless the excess deferral is distributed before April 15 of the following year, it will be taxed again in the year distributed. Income on the excess deferral distributed by April 15 of the immediately succeeding year will be treated, for federal income tax purposes, as earned and received by you in the tax year in which the contribution is made.

The total amount of contributions that a participant makes together with any employer contributions made on behalf of the participant in one year is limited to the lesser of 100% of Compensation or, for 2025, $70,000, or if applicable, $77,500 including catch-up contributions.

Rollovers. Participants may make a rollover contribution of an eligible rollover distribution from any other qualified retirement plan or an individual retirement arrangement (“IRA”). These funds will be maintained in a separate rollover account in which participants will have a nonforfeitable vested interest.

Benefits Under the 401(k) Plan

Vesting. At all times, participants have a fully vested, nonforfeitable interest in elective deferral contributions, safe harbor contributions and rollover contributions. Participants vest in employer contributions under the 401(k) Plan at the rate of 20% per year of service beginning after two years of service; so that they are fully vested after six years of service. Participants will also become fully vested in their entire account in the event they attain normal retirement age (age 65). Participants that terminate employment before they are 100% vested will forfeit the non-vested portion of their account upon the later of the date they incur five consecutive one-year breaks in service or the date they receive a distribution of the vested portion of their account.

Distribution at Termination of Employment. You (or your beneficiary, in the event of your death) will be entitled to receive a distribution of the vested amounts in your account when your employment terminates for any reason. Your benefit will be equal to the vested balance of your account. You will receive payment of your benefit in a lump sum. You may request a partial distribution of the vested portion of your account; the minimum amount will be $1,000. You may be eligible to elect a direct rollover of your distribution to an IRA or another qualified plan to avoid current taxation of your benefit. The 401(k) Plan will make involuntary cash-out distributions of vested account balances of $1,000 or less. In determining the value of your vested account balance, the Plan will include rollover contributions. If the value of your vested account balance exceeds $1,000, you must consent to any distribution of such account balance. If you are not a 5% or more owner of your employer, your required benefit commencement date is the April 1^st following the close of the year in which the later occurs: you attain age 72 (age 70 ½ if you were born on or before June 30, 1949) or you terminate employment.

Distribution after Death of Participant. In the event of your death, the value of your entire account will be payable to your beneficiary in accordance with the 401(k) Plan.

Investment of Contributions and Account Balances

All amounts credited to your accounts under the 401(k) Plan are held in the 401(k) Plan trust (the “Trust”), which is administered by the trustee appointed by Marathon Bank’s Board of Directors. Before the effective date of the stock offering, you are currently given the opportunity to direct the investment of your account into one or more of the following investment options:

In connection with the stock offering, the 401(k) Plan now provides that, in addition to the investment options specified above, you may direct the trustee, or its representative, to invest all or a portion of your account in the Marathon Bancorp Stock Fund.

Performance History

The following table provides performance data with respect to the investment funds in the 401(k) Plan as of December 31, 2023:

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Description of the Investment Funds

The following is a description of each of the funds:

American Funds The Growth Fund of America (GFA). This fund seeks growth of capital. American Funds' multiple portfolio counselor system allows each investment professional to implement his or her best investment ideas and helps to provide diversification for the overall portfolio. The Fund's investment professionals look for companies that offer the potential to provide strong earnings growth. Investments include the traditional growth company, as well as opportunities in cyclical companies and those in a turnaround situation that appear to be under-valued. The management of this Fund is more conservative than the traditional growth portfolio with more aversion to the risk inherent in the peer group.

Fidelity Contra Fund (CON). This fund seeks to achieve capital appreciation. The underlying fund invests in companies whose value the manager believes is not fully recognized by the public. These types of companies include companies that are experiencing positive fundamental change, such as a new management team or product launch, a significant cost-cutting initiative, a merger or acquisition, or a reduction in industry capacity that should lead to improved pricing. It may also include companies whose earnings potential has increased or is expected to increase more than generally perceived or those that have enjoyed recent market popularity but which appear to have fallen temporarily out of favor for reasons that are considered non-recurring or short-term. Lastly, the manager also considers companies that may be undervalued in relation to securities of other companies in the same industry. The Fund, as a result, is not constrained by any particular investment style and may tend to purchase both growth and value stocks. When purchasing securities, Fidelity relies on fundamental analysis of each issuer and its potential for success in light of its current financial condition, its industry position as well as economic and market conditions. Factors considered include growth potential, earnings estimates and management.

Mid Value Fund (MVF). This fund seeks long-term capital appreciation. The manager seeks to identify companies whose stock prices do not appear to reflect their underlying values. In selecting investments, the process begins with initial screens that look for mid-sized companies that have attractive fundamentals such as favorable industry structure, strong market position, and experienced management. From there, the manager conducts value and risk assessments to determine which companies to buy. The manager generally favors companies with one or more of the following: demonstrated or potentially attractive margins or cash-flow generation, sound balance sheet and financial management, employee stock ownership or low-stock price relative to earnings, cash flow, sales, net assets, book value, or private market value.

Mid Cap Index Fund (MCI). This fund seeks to achieve the approximate aggregate total return of a mid-cap U.S. domestic equity market index. The managers try to match the performance of the S&P Mid Cap 400 Index by holding all, or a representative sample of, the securities that comprise the Index. Although slight differences may exist in the short term, the Mid Cap Index portfolio and the S&P Mid Cap 400 Index are expected to perform similarly over the long run.

Vanguard Mid-Cap Growth ETF (VOT). This fund seeks to track the performance of the CRSP US Mid Cap Growth Index that measures the investment return of mid-capitalization growth stocks. The fund is an exchange-traded share class of Vanguard Mid-Cap Growth Index Fund, which employs an indexing investment approach designed to track the performance of the CRSP US Mid Cap Growth Index, a broadly diversified index of growth stocks of mid-size U.S. companies. The fund attempts to replicate the target index by investing all, or substantially all, of its assets in the stocks that make up the index, holding each stock in approximately the same proportion as its weighting in the index.

Vanguard Small Cap Value Index Fund (VIS). This fund seeks to track the performance of a benchmark index that measures the investment return of small-capitalization value stocks. The underlying fund employs a “passive management” or indexing-investment approach designed to track the performance of the CRSP US Small Cap Value Index, a broadly diversified index of value stocks of smaller U.S. companies. The Fund attempts to replicate the target index by investing all, or substantially all, of its assets in the stocks that make up the Index, holding each stock in approximately the same proportion as its weighting in the Index.

T. Rowe Price Small Cap Value Fund (MSO). This fund seeks long-term growth of capital. The manager utilizes a contrarian, bottom-up approach to identify underfollowed companies that are inefficiently priced. The strategy's broad diversification helps to control risk while the low turnover and patient orientation helps the manager fully exploit market inefficiencies. T. Rowe Price's managers seek securities they believe are undervalued as measured by assets, earnings, cash flow or business franchises. In selecting investments, they generally look for low price-book, price-earnings and price-cash flow ratios and an above-average dividend yield. Most companies will exhibit experienced management, a sound balance sheet and other positive financial characteristics.

Vanguard Explorer Fund (EXP). This seeks long-term capital appreciation. The underlying fund invests in a diversified group of small-company stocks with prospects for above-average growth. The Fund is managed by six advisors, each of whom runs its portion independently - although all emphasize small-capitalization stocks. Management of the fund is divided between Granahan Investment Management, Inc., Wellington Management Company, LLP, Chartwell Investment Partners, Grantham, Mayo, Van Otterloo & Co. LLC, Kalmar Investment Advisers and The Vanguard Group, Inc. The managers apply both fundamental and quantitative techniques in picking companies. Current strategies of this fund are: to invest in companies with prospects for superior growth; invest across many sectors that provide a diverse group of holdings; commonly invests over 60% of the fund in the Technology, Consumer Discretionary and Health Care sectors.

T. Rowe Price Equity Income Fund (D&G). This fund seeks to provide substantial dividend income and long-term capital appreciation. This portfolio is managed with a conservative, value-oriented approach that uses fundamental research to find undervalued stocks along with stocks that pay above average dividends. T. Rowe Price narrows the universe of companies down to approximately 300-400 companies by screening for market capitalization, liquidity, valuation characteristics (such as price-earnings, price-book and price-sales), and earnings and dividend streams that appear to be mispriced. Management conducts traditional fundamental analysis and rigorously evaluate companies to find undervalued companies across a range of industries. They focus on large capitalization companies that are either at discounts to historical valuations or undervalued based on relative valuations and have the ability to benefit from changes in investor perception or the emergence of a catalyst.

500 Index Fund (IND). This fund seeks to achieve the approximate aggregate total return of a broad U.S. domestic equity market index. John Hancock Asset Management's managers try to match the performance of the S&P 500 Index by holding all, or a representative sample of, the securities that comprise the Index. Although slight differences may exist in the short term, the 500 Index portfolio and the S&P 500 Index are expected to perform similarly over the long run.

American Funds Fundamental Investors (AFI). This fund seeks long-term growth of capital and income. Using principles of fundamental analysis, the underlying fund seeks undervalued and overlooked opportunities with the potential for long-term growth. Companies under consideration for the portfolio often have strong balance sheets, high-quality products and leading market share. The Fund's holdings typically represent good value and possess above-average potential for growth in sales, earnings and dividends. American Funds’ multiple portfolio counselor system allows each investment professional to implement his or her best investment ideas and helps to provide diversification for the overall portfolio.

American Funds The Investment Company of America (ICA). This fund seeks to achieve long-term growth of capital and income. The portfolio's investment professionals strive to buy stocks of well-managed companies at reasonable prices and hold them for the long term. The portfolio focuses its investments in well-established blue chip companies, representing a wide cross-section of the U.S. economy. The flexibility to invest in cash may provide a cushion in poor equity markets. The portfolio's low turnover rate is indicative of management's long-term, value-oriented approach to investing in stocks.

American Funds Washington Mutual Investors Fund (WMI). This fund seeks to produce income and to provide an opportunity for growth of principal consistent with sound common stock investing. In the selection of securities for investment, the Fund's portfolio counselors consider companies that currently pay dividends, have the potential to pay future dividends, and companies that offer the potential for long-term capital appreciation. The Fund strives to achieve an overall portfolio with above-average yield and a below-average price-to-earnings ratio in relation to the S&P 500 Index. The Fund has an eligible list of securities in which it may invest, governed by a strict set of financial standards. The Fund may not invest in securities that derive their primary revenues from alcohol or tobacco.

Franklin Mutual Beacon Fund (MCV). This fund seeks capital appreciation with income as a secondary goal. This underlying fund invests in stocks selling at a substantial discount to what the managers believe is their true intrinsic value. Consequently, the portfolio is constructed from the bottom up (using company specific criteria). Investments are made primarily in three areas: (1) inexpensive stocks based on asset value; (2) mergers, recapitalizations, spin-offs and other extraordinary corporate changes; and (3) bankruptcy and other financially distressed situations. This portfolio generally focuses on medium- and large-sized companies. This fund is considered a “deep value” fund that tends to perform well when the value investing style is in favor.

American Funds Capital World Growth and Income Fund (CGI). This fund seeks to provide long-term growth of capital with current income. The portfolio is conservatively managed and focuses on established companies that pay regular dividends and represent average long-term investment opportunities. The managers have significant flexibility to take advantage of opportunities around the world, investing primarily in blue chip stocks issued by companies in the world’s largest stock markets. Securities may be sold when the management team believes they no longer represent relatively attractive investment opportunities.

Templeton World Fund (DIV). This fund seeks long-term capital appreciation. The managers apply a “bottom-up”, value-oriented, long-term approach, focusing on the market price of a company’s securities relative to the manager’s evaluation of the company’s long-term earnings, asset value and cash flow potential. The managers also consider and analyze various measures related to stock valuation, such as a company’s price/cash flow ratio, price/earnings ratio, profit margins and liquidation value. Their long-term approach focuses on companies with strong outlooks for earnings and/or asset growth over a 5-year horizon. The team works closely together, drawing on the experience of analysts based in different offices around the world to arrive at a bargain list of attractively valued stocks. The ‘bargain list’ contains 100 to 200 stocks that the managers believe are undervalued. From that list, they select stocks based on the portfolio’s investment criteria and their individual research.

American Funds EuroPacific Growth Fund (EPG). This fund seeks long-term growth of capital. The underlying fund’s investment professionals seek to provide, in aggregate, a well-diversified and moderately aggressive portfolio through patient stock picking. Management tends to show strong conviction in their holdings and takes a long-term investment approach, often recognizing market contractions as buying opportunities. The Fund invests in securities of growing companies based primarily in Europe and the Pacific Basin. Holdings may range from small firms to large corporations. Under normal market conditions, the portfolio will invest almost all its assets in securities of issuers based outside the United States. The portfolio may invest in securities of issuers based in developing countries.

Invesco Global Fund (WWF). This fund seeks capital appreciation. In selecting securities the manager looks primarily for foreign and U.S. companies with high growth potential. He uses fundamental analysis of a company's financial statements, management structure, operations and product development, and considers factors affecting the industry of which the company is part. The portfolio manager also considers overall and relative economic conditions in the U.S. and foreign markets and seeks broad portfolio diversification in different countries. The manager is currently focused on companies that stand to benefit from global growth trends, businesses with strong competitive positions and high demand for their products or services, and cyclical opportunities in the business cycle and sectors or industries that may benefit from those opportunities. In applying these criteria, the manager considers the effect of worldwide trends on the growth of various business sectors. The trends, or “themes”, currently considered include the development of new technologies, corporate restructuring, the growth of mass affluence, and demographic changes.

Invesco Oppenheimer International Growth Fund (OIG). This fund seeks long-term capital appreciation. It seeks to invest in foreign companies with high growth potential. Using a bottom up investment approach, the portfolio manager first looks at the investment performance of individual stocks before considering the impact of general or industry-specific economic trends. This approach includes fundamental analysis of a company's financial statements and management structure and consideration of the company's operations and product development, as well as its position in the industry. Then the portfolio manager considers the effect of worldwide trends on the growth of particular business sectors and looks for companies that may benefit from those trends. The result is a diversified portfolio ranging from 50-100 holdings.

High Yield Fund (HYF). This fund seeks to realize an above-average total return over a market cycle of three to five years, consistent with reasonable risk. The investment team relies on the ability to integrate superior fundamental credit research with accurate relative value analysis to drive performance in the High Yield strategy. Management utilizes both a top-down and bottom-up approach within their investment process. Beginning with a top-down approach, Western Asset will consider their economic assessments along with each credit analyst's industry insights. A strategic portfolio is then created by management, which outlines the risk profile versus the benchmark highlighting key over- or underweights. Next, a bottom-up approach is utilized, which takes into consideration both fundamental credit analysis and a relative value assessment for each security within the strategic portfolio in order to construct the final client portfolio. Sell discipline is primarily based on at least one of three factors: (i) a security meets or exceeds its relative target value, (ii) the risk associated with holding the security no longer justifies the expected return, and (iii) there has been a relevant change to management’s original premise that affects their fundamental valuation.

PIMCO Real Return Fund (PRR). This fund seeks maximum real return (total return after inflation) consistent with preservation of real capital and prudent investment management. The underlying fund offers a broad exposure to technology which includes small-, mid-, and large capitalization companies in both international and domestic markets. PIMCO seeks to add value through a variety of techniques that attempt to maximize return and minimize volatility. The manager focuses on duration management to control yield curve exposure according to the firm's general investment outlook. In addition to the U.S. Treasury Inflation-Protected Security holdings, the manager may also utilize a sector rotation strategy, allowing the Fund to invest in U.S. corporate bonds and hedged, non-U.S. Inflation-Protected Securities in an attempt to add value. The manager may also use futures contracts to replicate bond positions, offering the potential to outperform physical bond securities.

Fidelity Advisor Total Bond Fund (FBF). This fund seeks a high level of current income. The fund normally invests at least 80% of assets in debt securities of all types and repurchase agreements for those securities. The manager uses the Bloomberg Barclays U.S. Universal Bond Index as a guide in allocating assets across the investment-grade, high yield, and emerging market asset classes. It invests up to 20% of assets in lower-quality debt securities (those of less than investment-grade quality, also referred to as high yield debt securities or junk bonds).

Opportunistic Fixed Income Fund (GLB). This fund seeks to achieve maximum total return, consistent with preservation of capital and prudent investment management. In order to achieve its investment objective, the manager seeks to: Invest across multiple asset types, geographies, credit tiers, and time horizons; Provide timely and dynamic exposure to a portfolio of global fixed income securities consisting of sovereign debt, inflation-linked bonds, corporate and high yield credit, securitized debt, bank loans and floating rate loans and emerging markets debt, convertible and hybrid securities; Manage the fund’s overall performance volatility within a range as reflected by the Bloomberg Global Aggregate Bond Index hedged to USD over the medium to long-term; Generate total returns through three main approaches: strategic sector positioning, market-neutral strategies, and tactical asset allocation: The strategic sector component of the portfolio provides exposure to non-core investment opportunities (e.g. emerging markets debt, high yield credit, bank loans etc.) that are designed to capture the repricing of long-term structural themes in the business cycle; The market neutral component of the portfolio is primarily expressed via relative value positioning, aimed at providing incremental return with low correlation to the direction of global fixed income markets. Market neutral positions are typically taken on interest rates, currencies, corporate and high yield credit, and emerging market debt positions; and Tactical asset allocation is used to capture both short- and medium-term dislocations in the market. Tactical opportunities are primarily expressed via sector rotation, country selection, security selection, currency management strategies and duration management strategies. Combine the three approaches noted above in a holistic manner while managing aggregate portfolio risk.

American Funds Target Date Retirement Funds. Depending on the proximity to its target date, the fund will seek to achieve the following objectives to varying degrees: growth, income and conservation of capital. The fund will increasingly emphasize income and conservation of capital by investing a greater portion of its assets in bond, equity-income and balanced funds as it approaches and passes its target date. In this way, the fund seeks to balance total return and stability over time. The fund will attempt to achieve its investment objectives by investing in a mix of American Funds in different combinations and weightings. The underlying American Funds represent a variety of fund categories such as growth funds, growth-and income funds, equity-income funds and a balanced fund and bond funds. The fund categories represent differing investment objectives. For example, growth funds seek long-term growth primarily through investing in both U.S. stocks and stocks of issuers domiciled outside the U.S. Growth-and-income funds seek long-term growth and income primarily through investments in stocks. Equity-income and balanced funds generally strive for income and growth through stocks and/or bond investments, while bond funds seek current income through bond investments. The fund is designed for investors who plan to retire in, or close to, the year designated in the fund’s name.

John Hancock Multimanager Aggressive Lifestyle Portfolio (ALS). This fund seeks to achieve long-term growth of capital by investing 100% of the portfolio's assets in underlying portfolios that invest primarily in equity securities. This asset allocation portfolio is managed with the intention of providing an optimal mix of a broadly diversified portfolio. There are four main steps involved in the design of the John Hancock Lifestyle Funds. First, asset classes and underlying funds are selected for potential inclusion in the portfolios. Next, sophisticated optimization techniques are used to establish the appropriate weightings given to each asset class. In the third step, an advanced statistical process is used to determine the optimal mix of managers. In the fourth and final step, the economic environment and investment markets are continually monitored to determine if any changes are needed, and to keep the portfolio up-to-date and consistent with its investment policies and objectives.

John Hancock Multimanager Growth Lifestyle Portfolio (GLS). This fund seeks long-term growth of capital by investing approximately 80% of the portfolio's assets in underlying portfolios that invest primarily in equity securities and approximately 20% of its assets in portfolio's that invest primarily in fixed-income securities. Current income is also a consideration. This asset allocation portfolio is managed with the intention of providing an optimal mix of a broadly diversified portfolio. There are four main steps involved in the design of the John Hancock Lifestyle Funds. First, asset classes and underlying funds are selected for potential inclusion in the portfolios. Next, sophisticated optimization techniques are used to establish the appropriate weightings given to each asset class. In the third step, an advanced statistical process is used to determine the optimal mix of managers. In the fourth and final step, the economic environment and investment markets are continually monitored to determine if any changes are needed, and to keep the portfolio up-to-date and consistent with its investment policies and objectives.

John Hancock Multimanager Balanced Lifestyle Portfolio (BLS). This fund seeks to achieve a balance between a high level of current income and growth of capital, with a greater emphasis on growth of capital, by investing approximately 40% of the portfolio's assets in underlying portfolios that invest primarily in fixed-income securities and approximately 60% of its assets in underlying

portfolios that invest primarily in equity securities. This asset allocation portfolio is managed with the intention of providing an optimal mix of a broadly diversified portfolio. There are four main steps involved in the design of the John Hancock Lifestyle Funds. First, asset classes and underlying funds are selected for potential inclusion in the portfolios. Next, sophisticated optimization techniques are used to establish the appropriate weightings given to each asset class. In the third step, an advanced statistical process is used to determine the optimal mix of managers. In the fourth and final step, the economic environment and investment markets are continually monitored to determine if any changes are needed, and to keep the portfolio up-to-date and consistent with its investment policies and objectives.

John Hancock Multimanager Moderate Lifestyle Portfolio (MLS). This fund seeks to achieve a balance between a high level of current income and growth of capital, with a greater emphasis on income by investing approximately 60% of the portfolio's assets in underlying portfolios that invest primarily in fixed-income securities and 40% of its assets in portfolios that invest primarily in equity securities. This asset allocation portfolio is managed with the intention of providing an optimal mix of a broadly diversified portfolio. There are four main steps involved in the design of the John Hancock Lifestyle Funds. First, asset classes and underlying funds are selected for potential inclusion in the portfolios. Next, sophisticated optimization techniques are used to establish the appropriate weightings given to each asset class. In the third step, an advanced statistical process is used to determine the optimal mix of managers. In the fourth and final step, the economic environment and investment markets are continually monitored to determine if any changes are needed, and to keep the portfolio up-to-date and consistent with its investment policies and objectives.

John Hancock Multimanager Conservative Lifestyle Portfolio (CLS). This fund seeks to achieve a high level of current income with some consideration given to growth of capital by investing approximately 80% of the portfolio's assets in underlying portfolios that invest primarily in fixed-income securities and 20% of its assets in underlying portfolios that invest primarily in equity securities. This asset allocation portfolio is managed with the intention of providing an optimal mix of a broadly diversified portfolio. There are four main steps involved in the design of the John Hancock Lifestyle Funds. First, asset classes and underlying funds are selected for potential inclusion in the portfolios. Next, sophisticated optimization techniques are used to establish the appropriate weightings given to each asset class. In the third step, an advanced statistical process is used to determine the optimal mix of managers. In the fourth and final step, the economic environment and investment markets are continually monitored to determine if any changes are needed, and to keep the portfolio up-to-date and consistent with its investment policies and objectives.

American Funds New World Fund (ANW). This fund seeks long-term capital appreciation. The investment professionals construct a broadly diversified portfolio with significant exposure to developing markets by investing in securities of issuers based in “qualified developing countries,” as well as in equity securities of issuers based in the developed world with significant assets or revenues attributable to developing countries. For their total return potential, the portfolio also invests in bonds offering exposure to developing countries. Management tends to show strong conviction in their holdings and takes a long-term investment approach, often recognizing market contractions as buying opportunities.

Invesco Developing Markets Fund (DMK). This fund seeks capital appreciation. The portfolio manager invests in emerging market businesses that appear likely to grow at a faster pace than world GDP and may benefit from distinctive structural global growth themes that Oppenheimer calls MANTRA®: Mass Affluence, New Technology, Restructuring and Aging. Within this framework, the portfolio manager relies on fundamental analysis to search for exceptional businesses with sustainable competitive advantages, strong management and high returns on capital.

Real Estate Securities Fund (REF). This fund seeks a combination of long-term capital appreciation and current income. The team uses both top-down and bottom-up research, looking for real estate securities it believes will provide superior returns to the portfolio, and attempts to focus on companies with the potential for stock price appreciation and a record of paying dividends. The team tracks economic conditions and real estate market performance in major metropolitan areas and analyzes performance of various property types within those regions, including Office, Multi-Family, Retail, Regional Malls, Industrial and Hotels. To perform this analysis, the managers use information from a nationwide network of real estate professionals. Their analysis also includes the companies’ management structures, financial structures, and business strategies. The goal of this analysis is to determine which of the issuers the managers believe will be the most profitable to the fund over the long term. The managers also consider the effect of the real estate securities markets in general when making investment decisions.

Vanguard Energy Fund (VEN). This fund seeks long-term capital appreciation. The investment team considers stocks of companies engaged in the production, transmission, marketing, or research of energy. Investment decisions tend to be value-oriented and are based on two factors: analysis of the world natural resource markets and fundamental research. Macroanalysis considers supply and demand trends, commodity prices and technological innovations. Fundamental research, performed by an experienced

team of analysts, emphasizes companies’ cash flow, asset values, earnings power, management and historical financial performance. The final portfolio is diversified by subsector and is generally about 40 percent international.

John Hancock Stable Value Fund (MSV). This fund seeks to preserve capital and provide stability of principal while earning current income that exceeds money market rates over the long term. The John Hancock Stable Value Fund is invested primarily in benefit responsive contracts issued by state regulated insurance companies and banks, including but not limited to John Hancock Life & Health Insurance Company. In addition, each insurance company either contractually guarantees or obtains contractual guarantees from third parties insuring against the loss of principal deposited into the Fund and providing that individual participant withdrawals will be paid promptly at book value (i.e., the amount of participant contributions plus interest previously credited, less previous withdrawals) even if the Fund’s total book value exceeds the market value of its underlying securities. However, if the book value of the Fund exceeds the market value of underlying securities, the stabilizing agreements provide that the payment of certain withdrawals may be delayed for up to 12 months unless the plan or the participant requesting the withdrawal elects to accept such payment subject to a market value adjustment. Before investing you should review the Fund’s Offering Memorandum. Plans that select the Fund may not select any “competing fund” in their plan.

Marathon Bancorp Stock Fund (Current Employer Stock Fund).  The Marathon Bancorp Stock Fund consists primarily of common stock of Marathon Bancorp. This fund was made available to 401(k) Plan participants in connection with the mutual holding company reorganization and minority stock offering in 2021. Participants were allowed the opportunity to invest 401(k) Plan funds in the Marathon Bancorp Stock Fund. Investments in the Marathon Bancorp Stock Fund involve special risks common to investments in the shares of common stock of Marathon Bancorp. Shares of Marathon Bancorp that were held in the Marathon Bancorp Stock Fund before the conversion and offering will be converted into new shares of common stock of Marathon Bancorp, in accordance with the exchange ratio. As soon as practicable after the closing of the stock offering, the Marathon Bancorp Stock Fund will be merged into the Marathon Bancorp Stock Fund.

An investment in any of the funds listed above is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. As with any mutual fund investment, there is always a risk that you may lose money on your investment in any of the funds listed above.

For a discussion of material risks you should consider, see “Risk Factors” of this prospectus supplement, “Risk Factors” beginning on page 16 of the attached prospectus, and the section of this prospectus supplement called “Notice of Your Rights Concerning Employer Securities” below.

Investors should carefully consider a mutual fund’s investment objectives, risks, charges, and expenses before investing. A prospectus, or summary prospectus if available, containing this and other information can be obtained by contacting the 401(k) Plan administrator. Read the prospectus carefully before investing.

Before directing retirement funds to a separate account, investors should carefully consider the investment objectives, risks, charges, and expenses of the separate account as well as their individual risk tolerance, time horizon and goals. For additional information, contact the 401(k) Plan administrator.

Marathon Bancorp, Inc. Stock Fund (New Employer Stock Fund).

In connection with the stock offering, you may, in the manner described earlier, elect to direct the trustee to invest all or a portion of your 401(k) Plan account in Marathon Bancorp common stock (other than account balances in the Marathon Bancorp Stock Fund). Your purchased shares will be held within the 401(k) Plan by the Marathon Bancorp Stock Fund. The Marathon Bancorp Stock Fund is neither a mutual fund nor a diversified or managed investment option. Rather, it is merely a recordkeeping mechanism established by the 401(k) Plan custodian to track the shares purchased by the participants in the stock offering through the 401(k) Plan.

Performance of the Marathon Bancorp Stock Fund depends on a number of factors, including the financial condition and profitability of Marathon Bancorp and Marathon Bank and market conditions for shares of Marathon Bancorp common stock generally.

Investments in the Marathon Bancorp Stock Fund involve special risks related to investments in the shares of common stock of Marathon Bancorp. In making a decision to invest all or a part of your account balance in the Marathon Bancorp Stock Fund, you should carefully consider the information set forth in this prospectus supplement under “Notice of Your Rights Concerning Employer Securities – The Importance of Diversifying Your Retirement Savings.”

For a discussion of material risks you should consider, see “Risk Factors” of this prospectus supplement, “Risk Factors” beginning on page 16 of the attached prospectus, and the section of this prospectus supplement called “Notice of Your Rights Concerning Employer Securities” below.

An investment in any of the investment options listed above under “Description of the 401(k) Plan – Description of the Investment Funds” is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. As with any investment option, there is always a risk that you may lose money on your investment in any of the investment options listed above.

Administration of the 401(k) Plan

The Trustee and Custodian. Nora Spatz and Joy Selting-Buchberger serve as trustee for all the investment funds under the 401(k) Plan, except for Marathon Bancorp Common Stock. First Trust of MidAmerica, services provided by Community Bank of Pleasant Hill, serves as trustee for the Marathon Bancorp Stock Fund.

401(k) Plan Administrator. Pursuant to the terms of the 401(k) Plan, the 401(k) Plan is administered by the 401(k) Plan administrator, which is Marathon Bank. The address of the 401(k) Plan administrator is 500 Scott Street, Wausau, Wisconsin 54403 and the telephone number at this address is (715) 845-7331. The 401(k) Plan administrator is responsible for the administration of the 401(k) Plan, interpretation of the provisions of the 401(k) Plan, prescribing procedures for filing applications for benefits, preparation and distribution of information explaining the 401(k) Plan, maintenance of 401(k) Plan records, books of account and all other data necessary for the proper administration of the 401(k) Plan, preparation and filing of all returns and reports relating to the 401(k) Plan which are required to be filed with the U.S. Department of Labor and the Internal Revenue Service, and for all disclosures required to be made to participants, beneficiaries and others under Sections 104 and 105 of ERISA.

Reports to Plan Participants. The 401(k) Plan administrator will furnish you a statement at least quarterly showing the balance in your account as of the end of that period, the amount of contributions allocated to your account for that period, and any adjustments to your account to reflect earnings or losses (if any). In addition, you may go online to www.jhgoenroll.com or call 1-800-395-1113 at any time to review your account balances.

Amendment and Termination

Marathon Bank intends to continue the 401(k) Plan indefinitely. Nevertheless, Marathon Bank may terminate the 401(k) Plan at any time. If the 401(k) Plan is terminated in whole or in part, then regardless of other provisions in the 401(k) Plan, you will have a fully vested interest in your 401(k) Plan account. Marathon Bank reserves the right to make any amendment or amendments to the 401(k) Plan which do not cause any part of the trust to be used for, or diverted to, any purpose other than the exclusive benefit of participants or their beneficiaries; provided, however, that Marathon Bank may make any amendment it determines necessary or desirable, with or without retroactive effect, to comply with ERISA.

Merger, Consolidation or Transfer

In the event of the merger or consolidation of the 401(k) Plan with another plan, or the transfer of the plan assets to another plan, the 401(k) Plan requires that, if the 401(k) Plan or the other plan terminates, you would receive a benefit immediately after the merger, consolidation or transfer which is equal to or greater than the benefit you would have been entitled to receive immediately before the merger, consolidation or transfer.

Federal Income Tax Consequences

The following is a brief summary of the material federal income tax aspects of the 401(k) Plan. You should not rely on this summary as a complete or definitive description of the material federal income tax consequences relating to the 401(k) Plan. Statutory provisions change, as do their interpretations, and their application may vary in individual circumstances. Finally, the consequences under applicable state and local income tax laws may not be the same as under the federal income tax laws. Consult your tax advisor with respect to any distribution from the 401(k) Plan and transactions involving the 401(k) Plan.

As a “tax-qualified retirement plan,” the Code affords the 401(k) Plan special tax treatment, including:

Marathon Bank will administer the 401(k) Plan to comply with the requirements of the Code as of the applicable effective date of any change in the law.

Lump-Sum Distribution. A distribution from the 401(k) Plan to a participant or the beneficiary of a participant will qualify as a lump-sum distribution if it is made within one taxable year, on account of the participant’s death, disability or separation from service, or after the participant attains age 59^1⁄₂, and consists of the balance credited to participants under the 401(k) Plan and all other profit sharing plans, if any, maintained by Marathon Bank. The portion of any lump-sum distribution required to be included in your taxable income for federal income tax purposes consists of the entire amount of the lump-sum distribution, less the amount of after-tax contributions, if any, you have made to this 401(k) Plan and any other profit-sharing plans maintained by Marathon Bank, which is included in the distribution.

Marathon Bancorp Common Stock Included in Lump-Sum Distribution. If a lump-sum distribution includes Marathon Bancorp common stock, the distribution generally will be taxed in the manner described above, except that the total taxable amount may be reduced by the amount of any net unrealized appreciation with respect to Marathon Bancorp common stock; that is, the excess of the value of Marathon Bancorp at the time of the distribution over its cost or other basis of the securities to the trust. The tax basis of Marathon Bancorp common stock, for purposes of computing gain or loss on its subsequent sale, equals the value of Marathon Bancorp common stock at the time of distribution, less the amount of net unrealized appreciation. Any gain on a subsequent sale or other taxable disposition of Marathon Bancorp common stock, to the extent of the amount of net unrealized appreciation at the time of distribution, will constitute long-term capital gain, regardless of the holding period of Marathon Bancorp common stock. Any gain on a subsequent sale or other taxable disposition of Marathon Bancorp common stock, in excess of the amount of net unrealized appreciation at the time of distribution, will be considered long-term capital gain. The recipient of a distribution may elect to include the amount of any net unrealized appreciation in the total taxable amount of the distribution, to the extent allowed by regulations to be issued by the Internal Revenue Service.

Distributions: Rollovers and Direct Transfers to Another Qualified Plan or to an IRA. You may roll over virtually all distributions from the 401(k) Plan to another qualified plan or to an individual retirement account in accordance with the terms of the other plan or account.

Notice of Your Rights Concerning Employer Securities

Federal law provides specific rights concerning investments in employer securities. Because you may in the future have investments in Marathon Bancorp common stock under the 401(k) Plan, you should take the time to read the following information carefully.

Your Rights Concerning Employer Securities. The 401(k) Plan must allow you to elect to move any portion of your account that is invested in Marathon Bancorp common stock from that investment into other investment alternatives under the 401(k) Plan. You may contact the 401(k) Plan administrator shown above for specific information regarding this right, including how to make this election. In deciding whether to exercise this right, you will want to give careful consideration to the information below that describes the importance of diversification. All of the investment options under the 401(k) Plan are available to you if you decide to diversify out of your investment in Marathon Bancorp common stock.

The Importance of Diversifying Your Retirement Savings. To help achieve long-term retirement security, you should give careful consideration to the benefits of a well-balanced and diversified investment portfolio. Spreading your assets among different types of investments can help you achieve a favorable rate of return, while minimizing your overall risk of losing money. This is because market or other economic conditions that cause one category of assets, or one particular security, to perform very well often cause another asset category, or another particular security, to perform poorly. If you invest more than 20% of your retirement savings in any one company or industry, your savings may not be properly diversified. Although diversification is not a guarantee against loss, it is an effective strategy to help you manage investment risk.

In deciding how to invest your retirement savings, you should take into account all of your assets, including any retirement savings outside of the 401(k) Plan. No single approach is right for everyone because, among other factors, individuals have different

financial goals, different time horizons for meeting their goals, and different tolerance for risk. Therefore, you should carefully consider the rights described here and how these rights affect the amount of money that you invest in Marathon Bancorp common stock through the 401(k) Plan.

It is also important to periodically review your investment portfolio, your investment objectives, and the investment options under the 401(k) Plan to help ensure that your retirement savings will meet your retirement goals.

Additional Employee Retirement Income Security Act, as amended, Considerations

As noted above, the 401(k) Plan is subject to certain provisions of ERISA, including special provisions relating to control over the 401(k) Plan’s assets by participants and beneficiaries. The 401(k) Plan’s feature that allows you to direct the investment of your account balances is intended to satisfy the requirements of Section 404(c) of ERISA relating to control over plan assets by a participant or beneficiary. The effect of this is two-fold. First, you will not be deemed a “fiduciary” because of your exercise of investment discretion. Second, no person who otherwise is a fiduciary, such as Marathon Bank, the 401(k) Plan administrator, or the 401(k) Plan’s trustee is liable under the fiduciary responsibility provision of ERISA for any loss which results from your exercise of control over the assets in your 401(k) Plan account.

Because you will be entitled to invest all or a portion of your account balance in the 401(k) Plan in Marathon Bancorp common stock, the regulations under Section 404(c) of the ERISA require that the 401(k) Plan establish procedures that ensure the confidentiality of your decision to purchase, hold, or sell employer securities, except to the extent that disclosure of such information is necessary to comply with federal or state laws not preempted by ERISA. These regulations also require that your exercise of voting and similar rights with respect to Marathon Bancorp common stock be conducted in a way that ensures the confidentiality of your exercise of these rights.

Securities and Exchange Commission Reporting and Short-Swing Profit Liability

Section 16 of the Securities Exchange Act of 1934 imposes reporting and liability requirements on officers, directors, and persons beneficially owning more than 10% of public companies, such as Marathon Bancorp. Section 16(a) of the Securities Exchange Act of 1934 requires the filing of reports of beneficial ownership. Within 10 days of becoming an officer, director or person beneficially owning more than 10% of the shares of Marathon Bancorp, a Form 3 reporting initial beneficial ownership must be filed with the Securities and Exchange Commission. Changes in beneficial ownership, such as purchases, sales and gifts generally must be reported periodically, either on a Form 4 within two business days after the change occurs, or annually on a Form 5 within 45 days after the close of fiscal year of Marathon Bancorp. Discretionary transactions in and beneficial ownership of Marathon Bancorp common stock by officers, directors and persons beneficially owning more than 10% of Marathon Bancorp common stock generally must be reported to the Securities and Exchange Commission by such individuals.

In addition to the reporting requirements described above, Section 16(b) of the Securities Exchange Act of 1934 provides for the recovery by Marathon Bancorp of profits realized by an officer, director or any person beneficially owning more than 10% of Marathon Bancorp common stock resulting from non-exempt purchases and sales of Marathon Bancorp common stock within any six-month period.

The Securities and Exchange Commission has adopted rules that provide exemptions from the profit recovery provisions of Section 16(b) for all transactions in employer securities within an employee benefit plan, provided certain requirements are met. These requirements generally involve restrictions upon the timing of elections to acquire or dispose of employer securities for the accounts of Section 16(b) persons.

Except for distributions of Marathon Bancorp common stock due to death, disability, retirement, termination of employment or under a qualified domestic relations order, persons affected by Section 16(b) are required to hold shares of Marathon Bancorp common stock distributed from the 401(k) Plan for six (6) months following such distribution and are prohibited from directing additional purchases of Marathon Bancorp common stock for six (6) months after receiving such a distribution.

Financial Information Regarding Plan Assets

Financial information representing the net assets available for 401(k) Plan benefits and the change in net assets available for 401(k) Plan benefits is available upon written request to the 401(k) Plan administrator at the address shown above.

LEGAL OPINION

The validity of the issuance of Marathon Bancorp common stock has been passed upon by Luse Gorman, PC, Washington, D.C., which firm has acted as special counsel to Marathon Bancorp in connection with the stock offering of Marathon Bancorp.

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PROSPECTUS

(Holding company for Marathon Bank)

Up to 1,897,500 Shares of Common Stock

(Subject to Increase to up to 2,182,125 Shares)

Marathon Bancorp, Inc., a Maryland corporation that we refer to as “Marathon Bancorp” throughout this prospectus, is offering shares of common stock for sale on a best-efforts basis in connection with the conversion of Marathon MHC from the mutual holding company to the stock holding company form of organization, effected by the merger of Marathon MHC with and into Marathon Bancorp. The shares we are offering represent the majority ownership interest in Marathon Bancorp currently owned by Marathon MHC, a Wisconsin-chartered mutual holding company. Marathon Bancorp’s common stock currently trades on the Pink Open Market operated by OTC Markets Group under the symbol “MBBC.” Upon completion of the conversion, we expect the shares of Marathon Bancorp common stock will trade on the Nasdaq Capital Market under the symbol “MBBC.” We are an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012.

The shares of common stock are first being offered for sale in a subscription offering to eligible members of Marathon MHC (i.e., eligible depositors of Marathon Bank, a Wisconsin-chartered savings bank) and to tax-qualified employee benefit plans of Marathon Bank. Shares not purchased in the subscription offering may be offered for sale to the general public in a community offering, with a preference given first to residents of the communities served by Marathon Bank. Any shares of common stock not purchased in the subscription or community offerings may be offered for sale to the public through a syndicate of broker-dealers, referred to in this prospectus as the syndicated community offering. The syndicated community offering may commence before the subscription and community offerings (including any extensions) have expired. However, no shares purchased in the subscription offering or the community offering will be issued until the completion of any syndicated community offering. We may sell up to 2,182,125 shares of common stock because of demand for the shares of common stock or changes in market conditions, without resoliciting subscribers. We must sell a minimum of 1,402,500 shares to complete the offering.

In addition to the shares we are selling in the offering, the shares of common stock of Marathon Bancorp currently owned by public stockholders will be exchanged for shares of common stock of Marathon Bancorp based on an exchange ratio that will result in existing public stockholders owning approximately the same percentage of common stock of Marathon Bancorp as they owned immediately before the completion of the conversion. We expect to issue up to 1,608,142 shares in the exchange.

The minimum purchase order is 25 shares. Generally, the maximum number of shares of common stock that can be ordered by any person, either individually or together with an associate or group of persons acting in concert, is 60,000 shares ($600,000) of common stock in all categories of the offering combined.

The subscription offering will expire at 3:00 p.m., Central Time, on March 21, 2025. If held, the community offering may begin concurrently with, during or after the subscription offering. We may extend the expiration date of the subscription and/or community offerings without notice to you until May 5, 2025, or longer if the Board of Governors of the Federal Reserve System, which we refer to as the “Federal Reserve Board” and the Wisconsin Department of Financial Institutions, which we refer to as the “WDFI,” approve a later date. No single extension may exceed 90 days and the offering must be completed by March 31, 2027. Once submitted, orders are irrevocable unless the subscription and community offerings are terminated or extended, with regulatory approval, beyond May 5, 2025, or the number of shares of common stock to be sold is increased to more than 2,182,125 shares or decreased to less than 1,402,500 shares. If the subscription and community offerings are extended past May 5, 2025, all subscribers will be notified and given the opportunity to confirm, change or cancel their orders. If you do not respond to the notice of extension, we will promptly return your funds with interest or cancel your deposit account withdrawal authorization. If the number of shares to be sold in the offering is increased to more than 2,182,125 shares or decreased to less than 1,402,500 shares, we will resolicit subscribers, and all funds delivered to us to purchase shares of common stock in the subscription and community offerings will be returned promptly with interest. Funds received in the subscription and the community offerings will be held in a segregated account at Marathon Bank and will earn interest at 0.05% per annum until completion or termination of the offering.

Janney Montgomery Scott LLC is assisting us in selling the shares on a best-efforts basis in the subscription and community offerings, and will serve as sole manager for any syndicated community offering. Janney Montgomery Scott LLC is not required to purchase any shares of common stock that are sold in the offering.

OFFERING SUMMARY

Price: $10.00 per share

This investment involves a degree of risk, including the possible loss of principal.

See “Risk Factors” beginning on page 16.

These securities are not deposits or savings accounts and are not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Neither the Securities and Exchange Commission, the Board of Governors of the Federal Reserve System, the Wisconsin Department of Financial Institutions, the Federal Deposit Insurance Corporation, nor any state securities regulator or commissioner has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

JANNEY MONTGOMERY SCOTT LLC

For assistance, contact the Stock Information Center at (312) 251-4342.

The date of this prospectus is [prospectus date].

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TABLE OF CONTENTS

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SUMMARY

The following summary explains the significant aspects of the conversion, the offering and the exchange of existing shares of Marathon Bancorp common stock for new shares of Marathon Bancorp common stock. It may not contain all of the information that is important to you. Before making an investment decision, you should read this entire document carefully, including the consolidated financial statements and the related notes, and the section entitled “Risk Factors.”

Our Organizational Structure and the Proposed Conversion and Stock Offering

Since 2021, we have operated in a two-tier mutual holding company structure. Marathon Bancorp is a Maryland corporation that is our publicly traded stock holding company and the parent company of Marathon Bank. At September 30, 2024, Marathon Bancorp had consolidated assets of $216.5 million, deposits of $172.2 million and stockholders’ equity of $31.6 million. Marathon Bancorp’s parent company is Marathon MHC, a Wisconsin-chartered mutual holding company. At September 30, 2024, Marathon Bancorp had 2,135,412 shares of common stock outstanding, of which 1,226,223 shares, or 57.4%, were owned by Marathon MHC, and the remaining 909,189 shares were held by the public.

Pursuant to the terms of the plan of conversion and reorganization, which we refer to as the “plan of conversion,” we are converting from the mutual holding company corporate structure to the fully public stock holding company corporate structure. Upon completion of the conversion, Marathon MHC will cease to exist. The conversion will be accomplished by the merger of Marathon MHC with and into Marathon Bancorp, with Marathon Bancorp surviving the merger. The shares of Marathon Bancorp common stock being offered for sale represent the majority ownership interest in Marathon Bancorp currently owned by Marathon MHC. Public stockholders of Marathon Bancorp will receive new shares of common stock of Marathon Bancorp in exchange for their current shares of Marathon Bancorp at an exchange ratio intended to preserve approximately the same aggregate ownership interest in Marathon Bancorp as public stockholders currently have in Marathon Bancorp, adjusted downward to reflect certain assets held by Marathon MHC, without giving effect to new shares purchased in the offering or cash paid in lieu of any fractional shares. The shares of Marathon Bancorp common stock owned by Marathon MHC will be canceled.

The following diagram shows our current organizational structure, reflecting ownership percentages at September 30, 2024:

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After the conversion and offering are completed, we will be organized as a fully public stock holding company, with the stock of Marathon Bancorp held as follows:

Our Business

Marathon Bank is a Wisconsin-chartered savings bank headquartered in Wausau, Wisconsin. Founded in 1902, we conduct our business from our main office and four branch offices, which are located in Marathon, Ozaukee and Waukesha Counties, Wisconsin. Our primary market area for deposits includes the communities in which we maintain our banking office locations, while our primary lending market area is broader and includes select businesses and customers in Southeastern Wisconsin. We are a community-oriented bank offering a variety of financial products and services to meet the needs of our customers. We believe that our community orientation and personalized service distinguishes us from larger banks that operate in our market area.

From our founding until 2014, we operated as a traditional thrift institution, offering primarily residential mortgage loans and savings accounts. In February 2014, we hired our current president and chief executive officer, Nicholas W. Zillges, and since this time we have strengthened and modernized our operations through upgrades to our credit, underwriting, information technology and compliance operations. Under the leadership of Mr. Zillges, we have developed a commercial real estate lending infrastructure, with a particular focus on expanding into the Southeastern Wisconsin market, including the Milwaukee metropolitan area, to grow our commercial real estate and multifamily loan portfolios. As part of our effort to expand into Southeastern Wisconsin, in 2024, we opened a new branch in Brookfield, Wisconsin and in 2018, we opened a branch in Mequon, Wisconsin. Additionally, consistent with our strategy to grow our commercial loan operations, we have enhanced our suite of deposit products, including remote deposit capture, commercial cash management and mobile deposits in order to accommodate business customers, and thereby grow our core deposits. While we have developed our commercial real estate platform in recent years, we also remain committed to our local community and intend to continue to be a significant one- to four-family residential mortgage lender in our market areas subject to market conditions and the interest rate environment.

Our business consists primarily of taking deposits from the general public and investing those deposits, together with funds generated from operations, in commercial and multifamily real estate loans, one- to four-family residential real estate loans and, to a lesser extent, commercial and industrial loans, construction loans and consumer loans. Subject to market conditions, we expect to continue our focus on originating commercial real estate and multifamily real estate loans in an effort to further increase the overall yield earned on our loans and assist in managing interest rate risk. We also invest in debt securities, which have historically consisted of mortgage-backed securities issued by U.S. government sponsored enterprises, municipal securities, corporate debt securities and U.S. government and agency securities. We offer a variety of deposit accounts, including checking accounts, savings accounts, money market accounts and certificate of deposit accounts. We borrow funds, primarily from the Federal Home Loan Bank of Chicago, to fund our operations as necessary.

Our executive office is located at 500 Scott Street, Wausau, Wisconsin 54403, and our telephone number at this address is (715) 845-7331. Our website address is www.marathonbank.com. Information on our website is not and should not be considered a part of this prospectus.

Business Strategy

Our business strategy is to operate as a well-capitalized and profitable community bank dedicated to providing personal service to our individual and business customers. We believe that we have a competitive advantage in the markets we serve because of our over 120-year history in the community, our knowledge of the local marketplace and our long-standing reputation for providing superior, relationship-based customer service. The following are the key elements of our business strategy:

Maintain our emphasis on commercial real estate lending with a focus on the higher growth Southeastern Wisconsin market. Following the completion of our mutual holding company reorganization and minority stock issuance in 2021, we began our expansion into the Southeastern Wisconsin market, including the Milwaukee metropolitan area, to increase our commercial real estate loans, including multifamily loans, which increased to $114.1 million, or 64.2% of our loan portfolio, at September 30, 2024, compared to $69.4 million, or 47.3% of our loan portfolio, at June 30, 2021. We intend to retain our presence as a commercial real estate lender (which includes multifamily loans) in our market area and seek to expand our market share in existing and other growth markets in Southeastern Wisconsin, including Milwaukee. We intend to continue to build relationships with small and medium-sized businesses and high net worth individuals in these market areas focusing on lending to manufacturing, wholesale distribution and professional service businesses. In addition, we expect to have approximately $120.6 million in maturing loans potentially repricing at higher interest rates by December 31, 2027 which may enhance net interest income. We believe the additional capital raised in the offering will enable us to lower our ratio of commercial real estate loans as a percentage of capital and allow us to continue measured growth of commercial real estate lending to new and existing customers. Given their larger balances and the complexity of the underlying collateral, commercial real estate and multifamily real estate loans generally have more risk than the owner-occupied one- to four-family residential real estate loans we originate. Because the repayment of commercial real estate and multifamily real estate loans depends on the successful management and operation of the borrower’s properties or related businesses, repayment of such loans can be affected by adverse conditions in the local real estate market or economy.

Continue to originate and sell certain residential real estate loans. Residential mortgage lending has historically been a significant part of our business, and we recognize that originating one- to four-family residential real estate loans is essential to our status as a community-oriented bank. Residential lending in our markets has declined in recent years due to the high-interest rate environment as the Federal Reserve Board has sought to reduce inflation nationwide by maintaining a high federal funds rate. During the year ended June 30, 2021, when interest rates were lower, we originated and sold $50.6 million of one- to four-family residential real estate loans held for sale for gains on sale of loans of $1.0 million. During the quarter ended September 30, 2024, during a period when interest rates were generally higher, we originated and sold $1.8 million of one- to four-family residential real estate loans held for sale for gains on sale of loans of $47,000. Similarly, during the year ended June 30, 2024, we originated and sold $4.4 million of one- to four-family residential real estate loans held for sale for gains on sale of loans of $175,000. As the Federal Reserve Board has begun to reduce interest rates and interest in residential lending may increase in future periods, subject to market conditions, we intend to increase our residential lending and continue to sell in the secondary market most of the long-term conforming fixed-rate one- to four-family residential real estate loans that we originate for fee income that enhances our non-interest income and mitigates the risks associated with changes in market interest rates that may adversely impact our interest income.

Increase our share of lower-cost core deposit growth. As interest rates increased in recent years, customers migrated to higher cost certificates of deposit. We have made a concerted effort in recent periods to begin to reduce our reliance on higher cost certificates of deposit in favor of obtaining lower cost retail and commercial deposit accounts. We also continue to enhance our technology-based deposit products such as remote deposit capture, commercial cash management and mobile deposits in order to accommodate business customers. This has had the effect of growing our core deposits (which is defined as our deposits other than certificates of deposit), which represented 60.1% of total deposits at September 30, 2024 up from 57.5% of total deposits at June 30, 2023. We intend to continue our focus on core deposit growth by offering our retail and commercial customers a full selection of deposit-related services, and making further investments in technology so that we can deliver high-quality, innovative products and services to our customers.

Manage credit risk to maintain a low level of non-performing assets. We believe that credit risk management is paramount to our long-term success. Over the past several years, we have invested significantly in both personnel and software to effectively manage our portfolio, and we have considerably enhanced our controls. We have established an experienced commercial credit team and we have implemented well-defined policies, a thorough and efficient loan underwriting process, and active credit monitoring. As a

result of our continued focus on credit risk management, we had no non-performing loans as of September 30, 2024. Our non-performing assets were $1.4 million or 0.65% of total assets at September 30, 2024 consisting of one real estate owned property. For further details, see “Business of Marathon Bank—Delinquencies and Asset Quality—Non-Performing Assets.” We intend to continue to support our investment in our commercial credit department as we grow our loan portfolio in the future.

Grow organically and through opportunistic bank or branch acquisitions or de novo branching. In addition to organic growth, we will also consider acquisition opportunities that we believe would enhance the value of our franchise and yield potential financial benefits for our stockholders. We believe opportunities exist to both increase our market share in our historical markets, and to continue our expansion into Southeastern Wisconsin. We will consider expanding our branch network through acquisitions and/or through establishing de novo branches, although we have no current acquisitions or specific new branches planned. We opened a new branch in Brookfield, Wisconsin in January 2024 as part of our expansion plans. The capital we are raising in the offering will provide us the opportunity to make acquisitions of other financial institutions or branches, and will also help fund improvements in our operating facilities.

Remain a community-oriented institution and rely on high quality service to maintain and build a loyal local customer base. We were established in 1902 and have been operating continuously since that time in our local community. Through the goodwill we have developed over the years of providing timely, efficient banking services, we believe that we have been able to attract a solid base of local retail customers on which we hope to continue to build our banking business.

Reasons for the Conversion and Offering

Our primary reasons for converting to the fully public stock form of ownership and undertaking the stock offering are to:

Terms of the Offering

We are offering for sale between 1,402,500 and 1,897,500 shares of common stock, to eligible members of Marathon MHC (i.e., eligible depositors of Marathon Bank), to our tax-qualified employee benefit plans and, to the extent shares remain available, in a community offering to the general public, with a preference given first to natural persons (including trusts of natural persons) residing in the Wisconsin Counties of Marathon, Ozaukee, Milwaukee and Waukesha. If necessary, we will also offer for sale shares to the general public in a syndicated community offering. The number of shares of common stock to be sold may be increased to up to 2,182,125 shares as a result of demand for the shares of common stock in the offering or changes in market conditions. Unless the number of shares of common stock to be offered is increased to more than 2,182,125 shares or decreased to fewer than 1,402,500 shares, or the subscription and community offerings are extended beyond May 5, 2025, subscribers will not have the opportunity to change or cancel their stock orders once submitted. If the subscription and community offerings are extended past May 5, 2025, all subscribers will be notified and given an opportunity to confirm, change or cancel their orders. All subscribers will be notified by mail sent to the address the subscriber provides on the stock order form they have submitted. If you do not respond to the notice of extension, your order will be cancelled and we will promptly return your funds with interest at 0.05% per annum or cancel your deposit account withdrawal authorization. If the number of shares to be sold is increased to more than 2,182,125 shares or decreased to less than 1,402,500 shares, all subscribers’ stock orders will be canceled, their withdrawal authorizations will be canceled and funds delivered to us to purchase shares of common stock in the subscription and community offerings will be returned promptly with interest at 0.05% per annum. We will then resolicit subscribers, giving them an opportunity to place new orders for a period of time. No shares purchased in the subscription offering and community offering will be issued until the completion of any syndicated community offering, if utilized.

The purchase price of each share of common stock offered for sale in the offering is $10.00. All investors will pay the same purchase price per share, regardless of whether the shares are purchased in the subscription offering, a community offering or a syndicated community offering. Investors will not be charged a commission to purchase shares of common stock in the offering. Janney Montgomery Scott, LLC, which we refer to as “Janney Montgomery Scott,” our marketing agent in the offering, will use its best efforts to assist us in selling shares of our common stock in the offering but is not obligated to purchase any shares of common stock in the offering.

How We Determined the Offering Range, the Exchange Ratio and the $10.00 Per Share Purchase Price

The amount of common stock we are offering for sale and the exchange ratio for the exchange of shares of Marathon Bancorp for new shares of Marathon Bancorp are based on an independent appraisal of the estimated market value of Marathon Bancorp, assuming the offering has been completed. RP Financial, LC. (“RP Financial”), our independent appraiser, has estimated that, as of November 8, 2024, the fully converted market value was $28.7 million, which represents the midpoint of the valuation range. Based on federal regulations, this market value forms the midpoint of a valuation range with a minimum of $24.4 million and a maximum of $33.0 million ($37.9 million at the adjusted maximum). Based on this valuation range from the appraisal, the 57.4% ownership interest of Marathon MHC in Marathon Bancorp as of September 30, 2024 being sold in the offering, certain assets held by Marathon MHC and the $10.00 per share price, the number of shares of common stock being offered for sale by Marathon Bancorp ranges from 1,402,500 shares to 1,897,500 shares. The purchase price of $10.00 per share was selected primarily because it is the price most commonly used in mutual-to-stock conversions of financial institutions. The exchange ratio ranges from 1.1368 new shares at the minimum of the offering range to 1.5381 (1.7688 at the adjusted maximum) new shares at the maximum of the offering range, and will generally preserve the percentage ownership of public stockholders in Marathon Bancorp immediately before the completion of the conversion. RP Financial will update its appraisal before we complete the conversion and offering. If, as a result of demand for the shares or changes in market conditions, RP Financial determines that our estimated pro forma market value has increased, we may sell up to 2,182,125 shares without further notice to you. If our pro forma market value at that time is either below $24.4 million or above $37.9 million, then, after consulting with the Federal Reserve Board and the WDFI, we may: terminate the offering and promptly return all funds with interest; set a new offering range and provide all subscribers the opportunity to place a new order; or take such other actions as may be permitted by the Federal Reserve Board, the WDFI and the Securities and Exchange Commission.

The appraisal is based in part on Marathon Bancorp’s financial condition and results of operations, the pro forma effect of the additional capital raised in the offering, and an analysis of a peer group of ten publicly traded savings and loan holding companies that RP Financial considers comparable to Marathon Bancorp consistent with regulatory guidelines applicable to the independent

valuation. The appraisal peer group consists of the following companies, all of which are traded on the Nasdaq Stock Market. Assets are as of September 30, 2024 other than as noted below.

In applying each of the valuation methods, RP Financial considered adjustments to the pro forma market value based on a comparison of Marathon Bancorp with the peer group. RP Financial made an upward adjustment for financial condition and a downward adjustment for asset growth. RP Financial made no adjustments for profitability, growth and viability of earnings, primary market area, dividends, liquidity of the shares, marketing of the issue, management, or effect of government regulations and regulatory reform. The upward adjustment applied for financial condition took into consideration the more favorable composition of Marathon Bancorp’s asset base, including a higher loans/assets ratio and higher equity/assets ratio. The downward adjustment applied for asset growth took into consideration Marathon Bancorp’s recent asset shrinkage, in comparison to the peer group’s recent growth.

The following table presents a summary of selected pricing ratios for Marathon Bancorp (on a pro forma basis) as of and for the twelve months ended September 30, 2024, and for the peer group companies based on earnings and other information as of and for the twelve months ended September 30, 2024 or most recent quarter available, with stock prices as of November 8, 2024, as reflected in the appraisal report. Compared to the average pricing of the peer group, and based upon the information in the following table, our pro forma pricing ratios at the midpoint of the offering range indicated a discount of 18.9% on a price-to-book value basis and a discount of 20.2% on a price-to-tangible book value basis. As Marathon Bancorp reported a net loss for the twelve months ended September 30, 2024, a valuation on a price-to-earnings basis is not meaningful.

The independent appraisal does not indicate trading market value. Do not assume or expect that our valuation as indicated in the appraisal means that after the conversion and offering the shares of our common stock will trade at or above the $10.00 per share purchase price. Furthermore, the pricing ratios presented in the appraisal were used by RP Financial to estimate our pro forma appraised value for regulatory purposes and not to compare the relative value of shares of our common stock with the value of the capital stock of the peer group. The value of the capital stock of a particular company may be affected by a number of factors such as financial performance, asset size and market location.

For a more complete discussion of the amount of common stock we are offering for sale and the independent appraisal, see “The Conversion and Offering—Stock Pricing and Number of Shares to be Issued.”

Effect of Marathon MHC’s Assets on Minority Stock Ownership

Public stockholders of Marathon Bancorp will receive new shares of common stock of Marathon Bancorp in exchange for their current shares of common stock of Marathon Bancorp pursuant to an exchange ratio that is designed to provide public stockholders with approximately the same ownership percentage of the common stock of Marathon Bancorp after the conversion as their ownership percentage immediately before the conversion, without giving effect to new shares purchased in the offering or cash paid in lieu of any fractional shares. However, the exchange ratio will be adjusted downward to reflect assets held by Marathon MHC (other than shares of common stock of Marathon Bancorp) at the completion of the conversion, which net assets consisted primarily of cash totaling $100,000 as of September 30, 2024.

The Exchange of Existing Shares of Marathon Bancorp Common Stock

If you are a stockholder of Marathon Bancorp immediately before the completion of the conversion and offering, your shares will be exchanged for new shares of common stock of Marathon Bancorp. The number of shares of common stock you will receive will be based on the exchange ratio, which will depend upon our final appraised value and the percentage of outstanding shares of Marathon Bancorp common stock owned by public stockholders immediately before the completion of the conversion and offering. The following table shows how the exchange ratio will adjust, based on the appraised value of Marathon Bancorp as of November 8, 2024, assuming immediately before the completion of the conversion and offering public stockholders of Marathon Bancorp own 42.4% of Marathon Bancorp common stock and Marathon MHC had assets (excluding its shares of Marathon Bancorp common stock) of $100,000. The table also shows the number of shares of Marathon Bancorp common stock a hypothetical owner of Marathon Bancorp common stock would receive in exchange for 100 shares of Marathon Bancorp common stock owned at the completion of the conversion and offering, depending on the number of shares of common stock issued in the offering.

No fractional shares of Marathon Bancorp common stock will be issued to any public stockholder of Marathon Bancorp. For each fractional share that otherwise would be issued, Marathon Bancorp will pay cash equal to the product obtained by multiplying the fractional share interest to which the holder otherwise would be entitled by the $10.00 per share offering price.

Outstanding options to purchase shares of Marathon Bancorp common stock will convert into and become options to purchase shares of Marathon Bancorp common stock based upon the exchange ratio. The aggregate exercise price, duration and vesting schedule of these options will be unaffected by the conversion. At September 30, 2024, there were 104,877 outstanding options to purchase shares of Marathon Bancorp common stock, 40,640 of which have vested. The outstanding options will be converted into

options to purchase 119,224 shares of common stock at the minimum of the offering range and 161,311 shares of common stock at the maximum of the offering range. Because federal regulations prohibit us from repurchasing our common stock during the first year following the conversion unless compelling business reasons exist to do so, we may use authorized but unissued shares to fund option exercises that occur during the first year following the conversion. If all existing options were exercised and funded with authorized but unissued shares of common stock following the conversion, stockholders would experience ownership dilution of approximately 5.44%.

Intended Use of the Proceeds from the Offering

We intend to (i) contribute at least 50% of the net proceeds from the offering to Marathon Bank, (ii) fund a loan to our employee stock ownership plan to finance its purchase of shares of common stock in the stock offering and (iii) retain the remainder of the net proceeds from the offering at Marathon Bancorp. Therefore, assuming we sell 1,650,000 shares of common stock in the stock offering at the midpoint of the offering range, and we have net proceeds of $14.9 million, we intend (i) to contribute $7.4 million to Marathon Bank, (ii) loan $1.3 million to our employee stock ownership plan to fund its purchase of shares of common stock and (iii) retain the remaining $6.1 million of the net proceeds at Marathon Bancorp.

Marathon Bancorp may use the funds it retains for investment in securities, to repurchase shares of common stock, to acquire other financial institutions, to pay cash dividends and for other general corporate purposes. Marathon Bank may use the proceeds it receives to support increased lending, support growth and the development of new products and services, expand its branch network by opening or acquiring new branches or by acquiring other financial institutions. We do not currently have any agreements or understandings regarding any acquisition or branch transactions.

See “How We Intend to Use the Proceeds from the Offering” for additional information.

Persons Who May Order Shares of Common Stock in the Offering

We are offering the shares of common stock for sale in a subscription offering in the following descending order of priority:

Shares of common stock not purchased in the subscription offering may be offered for sale to the general public in a community offering, with a preference given first to natural persons (including trusts of natural persons) residing in the Wisconsin Counties of Marathon, Ozaukee, Milwaukee and Waukesha, and then to Marathon Bancorp’s public stockholders at the close of business on January 31, 2025. The community offering, if any, may occur concurrently with, during or promptly after the subscription offering. We also may offer for sale shares of common stock not purchased in the subscription offering and the community offering in a syndicated community offering. Janney Montgomery Scott will act as sole manager for the syndicated community offering. We have the right to accept or reject, in whole or in part, in our sole discretion, orders received in the community offering or syndicated community offering, and our interpretation of the terms and conditions of the plan of conversion will be final. Any determination to accept or reject stock orders in the community offering or syndicated community offering will be based on the facts and circumstances available to management at the time of the determination.

If we receive orders for more shares than we are offering for sale, we may not be able to fill your order, either fully or partially. A detailed description of the subscription offering, the community offering and the syndicated community offering, as well as a discussion regarding allocation procedures, can be found in the section of this prospectus entitled “The Conversion and Offering.”

Limits on How Much Common Stock You May Purchase

The minimum number of shares of common stock that may be purchased is 25 shares.

Generally, no individual, or individuals acting through a single qualifying account held jointly, may purchase more than 60,000 shares ($600,000) of common stock. If any of the following persons purchase shares of common stock, their purchases, in all categories of the offering, when combined with your purchases, cannot exceed 60,000 shares ($600,000) of common stock:

Persons having the same residence or mailing address and persons exercising subscription rights through qualifying accounts registered to the same address at any of the eligibility, supplemental eligibility or voting record dates will be subject to the overall purchase limitation of 60,000 shares ($600,000).

In addition to the above purchase limitations, there is an ownership limitation for current stockholders of Marathon Bancorp other than our employee stock ownership plan. Shares of common stock that you purchase in the offering individually or together with persons described above, plus any shares you and they receive in exchange for existing shares of Marathon Bancorp common stock, may not exceed 9.9% of the total shares of common stock to be issued and outstanding after the completion of the conversion and offering. However, if, based on your current ownership level, you will own more than 9.9% of the total shares of common stock of Marathon Bancorp to be issued and outstanding after the completion of the conversion and offering following the exchange of your shares of common stock, you will be ineligible to purchase any new shares in the offering. You will be required to obtain regulatory approval or non-objection before acquiring 10% or more of Marathon Bancorp’s common stock.

Subject to regulatory approval, we may increase or decrease the purchase and ownership limitations at any time. See the detailed description of the purchase limitations in “The Conversion and Offering—Additional Limitations on Common Stock Purchases.”

How You May Purchase Shares of Common Stock in the Subscription Offering and the Community Offering

In the subscription offering and community offering, you may pay for your shares only by:

Cash will only be accepted at Marathon Bank’s main office and will be converted to a bank check. Please do not submit cash by mail. You may not use any type of third-party check to pay for shares of common stock. Wire transfers will not be accepted. Applicable regulations prohibit Marathon Bank from lending funds or extending credit to any person to purchase shares of common stock in the offering. You may not submit a Marathon Bank line of credit check. You may not designate withdrawal from a Marathon Bank account with check-writing privileges; rather, submit a check. If you request a withdrawal from an account with check-writing privileges, we reserve the right to interpret that as your authorization to treat those funds as if we had received a check for the designated amount, and will immediately withdraw the amount from the specified account(s). You may not authorize withdrawal from a Marathon Bank individual retirement account. See “—Using Individual Retirement Account Funds to Purchase Shares of Common Stock.”

You may subscribe for shares of common stock in the subscription and community offerings by delivering a signed and completed original stock order form, together with full payment payable to Marathon Bancorp, Inc. or authorization to withdraw funds from one or more of your Marathon Bank deposit accounts, provided that the stock order form is received (not postmarked) before 3:00 p.m., Central Time, on March 21, 2025, which is the expiration of the subscription offering period.

Your completed and signed stock order form and payment may be submitted to us by:

Hand delivery of stock order forms will be accepted only at the Stock Information Center. Do not deliver your stock order form to any other of Marathon Bank’s offices. The Stock Information Center is open Monday through Friday between 10:00 a.m. and 4:00 p.m., Central Time, except for bank holidays. Do not mail stock order forms to Marathon Bank’s offices.

See “The Conversion and Offering—Procedure for Purchasing Shares in the Subscription and Community Offerings—Payment for Shares” for a complete description of how to purchase shares in the subscription and community offerings.

Using Individual Retirement Account Funds to Purchase Shares of Common Stock

You may be able to subscribe for shares of common stock using funds in your IRA or other retirement account. If you wish to use some or all of the funds in your Marathon Bank IRA or other retirement account, the applicable funds must be transferred to a self-directed account maintained by an independent custodian or trustee, such as a brokerage firm, and the purchase must be made through that account. If you do not have such an account, you will need to establish one before placing your stock order. An annual administrative fee may be payable to the independent custodian or trustee. Because individual circumstances differ and the processing of retirement fund orders takes additional time, we recommend that you contact our Stock Information Center promptly, preferably at least two weeks before the March 21, 2025 offering deadline, for assistance with purchases using funds in your IRA or other retirement account you may have at Marathon Bank or elsewhere. Whether you may use such funds to purchase shares in the offering may depend on timing constraints and, possibly, limitations imposed by the institution where the funds are held.

See “The Conversion and Offering—Procedure for Purchasing Shares in the Subscription and Community Offerings—Payment for Shares” and “—Using Individual Retirement Account Funds” for a complete description of how to use IRA funds to purchase shares of common stock in the offering.

Market for Common Stock

Existing publicly held shares of Marathon Bancorp’s common stock are traded on the Pink Open Market operated by OTC Markets Group under the symbol “MBBC.” Upon completion of the conversion, the new shares of common stock of Marathon Bancorp will replace the existing shares, which we expect will trade on the Nasdaq Capital Market under the symbol “MBBC,” subject to compliance with certain conditions, including having 300 “round lot” stockholders (stockholders owning more than 100 shares) and at least three broker-dealers making a market for our common stock. As of January 31, 2025, Marathon Bancorp had 10 registered market makers in its common stock.

Payment of Dividends

Following completion of the stock offering, our board of directors will have the authority to declare dividends on our shares of common stock, subject to our capital requirements, our financial condition and results of operations, tax considerations, statutory and regulatory limitations, and general economic conditions. However, no decision has been made with respect to the amount, if any, and timing of any dividend payments. We cannot assure you that we will pay dividends in the future, or that any such dividends will not be reduced or eliminated in the future. For information regarding our proposed dividend policy, see “Our Dividend Policy.”

Purchases by Directors and Executive Officers

We expect our directors and executive officers, together with their associates, to subscribe for 32,500 shares of common stock in the offering, representing 2.3% of the shares to be sold at the minimum of the offering range. The purchase price paid by them will be the same $10.00 per share price paid by all other persons who purchase shares of common stock in the offering. Following the conversion and offering, our directors and executive officers, together with their associates, are expected to beneficially own 251,148 shares of common stock (including any stock options exercisable within 60 days of January 31, 2025), or 10.3% of our total outstanding shares of common stock at the minimum of the offering range, which includes shares they currently own in Marathon Bancorp that will be exchanged for new shares of Marathon Bancorp.

See “Subscriptions by Directors and Executive Officers” for more information on the proposed purchases of shares of common stock by our directors and executive officers.

Deadline for Orders of Shares of Common Stock in the Subscription and Community Offerings

The deadline for submitting orders to purchase shares of common stock in the subscription and community offerings is 3:00 p.m., Central Time, on March 21, 2025, unless we extend this deadline. If you wish to purchase shares of common stock, a properly completed and signed original stock order form, together with full payment, must be received (not postmarked) by this time.

Although we will make reasonable attempts to provide this prospectus and offering materials to holders of subscription rights, the subscription offering and all subscription rights will expire at 3:00 p.m., Central Time, on March 21, 2025, whether or not we have been able to locate each person entitled to subscription rights.

See “The Conversion and Offering—Procedure for Purchasing Shares in the Subscription and Community Offerings—Expiration Date” for a complete description of the deadline for purchasing shares in the stock offering.

You May Not Sell or Transfer Your Subscription Rights

Applicable regulations prohibit you from transferring your subscription rights. If you order shares of common stock in the subscription offering, you will be required to certify that you are purchasing the common stock for yourself and that you have no agreement or understanding to sell or transfer your subscription rights or the shares that you are purchasing. We intend to take legal action, including reporting persons to federal or state agencies, against anyone who we believe has sold or transferred his or her subscription rights. We will not accept your order if we have reason to believe you are attempting to sell or transfer your subscription rights to other individuals. On the stock order form, you cannot add the names of others for joint stock registration unless they are also named on your qualifying deposit account(s). Doing so may jeopardize your subscription rights. In addition, the stock order form requires that you list all deposit accounts you held at your date of eligibility, giving all names on each account and the account number at the applicable eligibility date. Failure to provide this information, or providing incomplete or incorrect information, may result in a loss of part or all of your share allocation.

Delivery of Shares of Common Stock

All shares of common stock sold will be issued in book entry form. Stock certificates will not be issued. A statement reflecting ownership of shares of common stock issued in the subscription and community offerings will be mailed by our transfer agent to the persons entitled thereto at the registration address noted by them on their stock order forms as soon as practicable following consummation of the conversion. We expect trading in the stock to begin on the day of completion of the conversion or the next business day. The conversion is expected to be completed as soon as practicable following satisfaction of the conditions described below in “—Conditions to Completion of the Conversion.” Until a statement reflecting your ownership of shares of common stock is available and delivered to you, you may not be able to sell the shares of common stock that you purchased in the offering, even though the common stock will have begun trading. Your ability to sell your shares of common stock before receiving your statement will depend on arrangements you may make with a brokerage firm.

Conditions to Completion of the Conversion

We cannot complete the conversion and offering unless:

Marathon MHC intends to vote its shares in favor of the plan of conversion. At the close of business on January 31, 2025, Marathon MHC owned 1,226,223 shares, or approximately 57.4%, of the outstanding shares of common stock of Marathon Bancorp. At the close of business on January 31, 2025, the directors and executive officers of Marathon Bancorp and their affiliates owned 167,041 shares of Marathon Bancorp (excluding exercisable options), or 7.8% of the outstanding shares of common stock and 18.4% of the outstanding shares of common stock excluding shares held by Marathon MHC. They intend to vote those shares in favor of the plan of conversion.

Steps We May Take if We Do Not Receive Orders for the Minimum Number of Shares

If we do not receive orders for at least 1,402,500 shares of common stock, we may take one or more steps to sell the minimum number of shares of common stock in the offering range. Specifically, we may:

If we extend the offering past May 5, 2025, all subscribers will be notified and given an opportunity to confirm, change or cancel their orders. If you do not respond to the notice of extension, we will cancel your stock order and promptly return your funds with interest for funds received in the subscription and community offering or cancel your deposit account withdrawal authorization. If one or more purchase limitations are increased, subscribers in the subscription offering who ordered the maximum amount will be given the opportunity to increase their subscriptions up to the then-applicable limit.

Possible Change in the Offering Range

RP Financial will update its appraisal before we complete the conversion and offering. If, as a result of demand for the shares or changes in market conditions, RP Financial determines that our pro forma market value has increased, we may sell up to 2,182,125 shares in the offering without further notice to you. If our pro forma market value at that time is either below $24.4 million or above $37.9 million (the minimum and adjusted maximum pro forma market value, respectively, based on the appraised value of Marathon Bancorp as of November 8, 2024), then, after consulting with the Federal Reserve Board and the WDFI, we may:

If we set a new offering range, we will promptly return funds, with interest at 0.05% per annum for funds received for purchases in the subscription and community offerings, and cancel any authorization to withdraw funds from deposit accounts for the purchase of shares of common stock. We will then resolicit subscribers, allowing them to place a new stock order for a specified period of time.

Possible Termination of the Offering

We may terminate the offering at any time before the special meeting of members of Marathon MHC and the special meeting of stockholders of Marathon Bancorp that have been called to vote on the conversion, and at any time after member and stockholder approval with regulatory approval. If we terminate the offering, we will promptly return your funds with interest at 0.05% per annum, and we will cancel deposit account withdrawal authorizations.

Benefits to Management and Potential Dilution to Stockholders Resulting from the Conversion

We expect our employee stock ownership plan, which is a tax-qualified retirement plan operated for the benefit of Marathon Bank’s employees, to purchase up to 8% of the shares of common stock we sell in the offering. However, if market conditions warrant, in the judgment of its trustee, the employee stock ownership plan’s subscription order may not be filled and the employee stock ownership plan may instead elect to purchase shares in the open market following the completion of the conversion, subject to the approval of the Federal Reserve Board and the WDFI.

We intend to implement one or more new stock-based benefit plans no earlier than six months after completion of the conversion. Stockholder approval of these plans will be required before implementation. We have not determined whether we will adopt the plans within or after 12 months following the completion of the conversion. If we implement stock-based benefit plans within 12 months following the completion of the conversion, the stock-based benefit plans would be limited to reserving a number of shares (1) up to 4% of the shares of common stock sold in the offering for awards of restricted stock or restricted stock units to employees and directors, at no cost to the recipients, and (2) up to 10% of the shares of common stock sold in the offering for issuance pursuant to the exercise of stock options by employees and directors. If the stock-based benefit plan is adopted more than 12 months after the completion of the conversion, it would not be subject to the percentage limitations set forth above. We have not yet determined the definitive number of shares that will be reserved for issuance under these plans. For a description of our current stock-based benefit plan, see “Management—Benefits to be Considered Following Completion of the Conversion—Stock-Based Benefit Plans.”

The following table summarizes the number of shares of common stock and the aggregate dollar value of grants that are available under one or more stock-based benefit plans if such plans reserve a number of shares of common stock equal to 4% and 10% of the shares sold in the stock offering for restricted stock awards or restricted stock units and stock options, respectively. The table shows the dilution to stockholders if all such shares are issued from authorized but unissued shares, instead of purchased in the open market. A portion of the stock grants shown in the table below may be made to non-management employees. The table also sets forth the number of shares of common stock to be acquired by the employee stock ownership plan for allocation to all qualifying employees.