Form 11-K Mayville Engineering For: Dec 31

Note 1. Description of Plan

The following description of the Mayville Engineering Company, Inc. 401(k) Plan (the Plan) provides only general information. Participants should refer to the Plan document for a more complete description of the Plan’s provisions.

General

The Plan is a defined contribution plan covering substantially all employees of Mayville Engineering Company, Inc. (the Company). The Plan is intended to be a qualified retirement plan under the Internal Revenue Code (IRC) and the purpose is to enable eligible employees to save for retirement. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974 (ERISA), as amended.

Eligibility

Employees become eligible to participate in the Plan for both employee and employer match contributions on the first entry date after an employee’s hire date. The entry dates of the Plan are January 1, April 1, July 1 and October 1.

Employees are also eligible to receive Company profit sharing contributions after they have completed 1,000 hours of service within a plan year and are employed by the Company on the last day of the Plan year. There are certain circumstances where the eligibility rules are waived including military leave, medical leave, retirement and death.

Contributions

Each year, participants may contribute up to 50% of pretax annual compensation, as defined by the Plan. Participants may elect to have any portion, or all of their contributions designated as Roth 401(k) contributions. Participants who have attained age 50 before the end of the Plan year are eligible to make catch-up contributions. Participants may also contribute amounts representing distributions from other qualified defined benefit or defined contribution plans (rollover). Participants direct the investment of their contributions into various investment options offered by the Plan. The Plan includes an auto-enrollment provision whereby all newly eligible employees are automatically enrolled in the Plan unless they affirmatively elect not to participate in the Plan. Automatically enrolled participants have their deferral rate set at 4% of eligible compensation and their contributions invested in a designated balanced fund until changed by the participant. The Plan also has a provision for auto-escalation of contribution rates of 1% each year, capped at 6%.

All Plan participants are eligible for employer matching contributions equal to 50% of the participant’s contributions up to a maximum of 6% of eligible compensation.

The Company can make a discretionary contribution of Company stock authorized by the Board of Directors. These Company discretionary contributions are usually approved at the end of each calendar year and funded in the subsequent year resulting in a contribution receivable on the Statements of Net Assets Available for Benefits. For a participant to be eligible for the Company discretionary contribution of Company stock, the participant must work 1,000 hours during the year and be employed at the end of the year. The Company did not make any discretionary contributions in the form of Company stock for the year ended December 31, 2025.

Contributions are subject to certain Internal Revenue Service (IRS) limitations.

Participant Accounts

Each participant’s account is credited with the participant’s contributions, Company’s contributions and Plan earnings. Participant accounts are charged with an allocation of administrative expenses that are paid by the Plan. Allocations are based on participant earnings, account balances or specific participant transactions, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant’s vested account balance.

Note 2. Summary of Significant Accounting Policies

Note 3. Plan Termination

Although it has not expressed any intent to do so, the Company has the right under the Plan to discontinue its contributions at any time and to terminate the Plan subject to the provisions of ERISA. In the event of Plan termination, participants would become 100% vested in their Company contributions.

Note 4. Plan Transfers

Plan transfers for the year ended December 31, 2025 consists of:

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ESOP Diversification: Plan participants who also participate in the Mayville Engineering Company, Inc. Employee Stock Ownership Plan (ESOP) and meet certain eligibility requirements of the ESOP are allowed to transfer a portion of their account balances from the ESOP to the Plan under the diversification provisions of the ESOP. Participants who have completed at least 10 years of service and have attained the age of 50 may elect to diversify their account balances and have the opportunity to transfer up to 50% of their ESOP balance into their Plan account during the next five-year period. After the five-year election period, additional transfers are allowed but are limited to 75% of their account balance.

In addition to the above, of the $6,145 of rollovers listed on the Statement of Changes in Net Assets Available for Benefits, $5,234 relate to rollover contributions from the ESOP.

Note 5. Fair Value Measurements

The framework for measuring fair value provides a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (level 1) and the lowest priority to unobservable inputs (level 3). The three levels of the fair value hierarchy are described as follows:

Level 1 – Inputs to the valuation methodology are unadjusted quoted prices for identical assets or liabilities in active markets that the Plan has the ability to access.

Level 2 – Inputs to the valuation methodology include:

Note 6. Tax Status

The Company adopted a prototype volume submitter profit sharing 401(k) Plan with a cash or deferral arrangement which received a letter from the IRS dated June 30, 2020, stating that the Plan and related trust are designed in accordance with applicable sections of the IRC. The Plan has been amended since receiving the opinion letter. The Plan Administrator believes that the Plan is designed, and is currently being operated, in compliance with the applicable requirements of the IRC and, therefore, believe that the Plan is qualified and the related trust is tax-exempt.

Note 7. Party-in-Interest and Related Party Transactions

Fees incurred by the Plan for investment management by Principal Financial Group, or its affiliates, are included in net appreciation in fair value of investments, as they are paid through revenue sharing, rather than a direct payment. Fees paid by the Plan

Note 8. Risks and Uncertainties

The Plan invests in various investment securities. Investment securities are exposed to various risks such as interest rate, market and credit risks. Due to the level of risk associated with certain investment securities, it is at least reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect participants’ account balances and the amounts reported in the Statements of Net Assets Available for Benefits.

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Schedule H, Line 4i – Schedule of Assets (Held at End of Year)

December 31, 2025

(in thousands)

Plan Sponsor: Mayville Engineering Company, Inc.

Plan Sponsor EIN: 39-0944729

Plan Number: 003

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* Represents a party-in-interest to the Plan.

** Information not required for participant directed investments

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See report of independent registered public accounting firm