A 401(k) compensation definition error happens when payroll calculates deferrals, match, or other contributions on a different pay base than the one written in your plan document, and bonuses are the most common place it shows up. For a plan sponsor this is a fiduciary operations problem, not a payroll rounding issue, because the plan document controls and the payroll system only follows instructions. This guide walks through how sponsors confirm what the document requires, size the error, and correct it with payroll and the recordkeeper.
1. Why a Bonus Mismatch Is a Fiduciary Problem
Your plan document defines which pay counts for deferrals, employer contributions, and testing. Payroll earning codes are configured by people who may never have read that definition. When the two disagree, the plan is not operated according to its terms, and that is an operational failure the sponsor must address.
1.1 The document controls, not the payroll setup
If the document includes bonuses in plan compensation and payroll excluded them, participants who elected a percentage were shorted. The reverse also happens: payroll includes a pay type the document excludes. Either direction is a failure. See our overview of plan document and operations mismatches for the broader pattern.
1.2 Why bonuses are the usual culprit
Bonuses are often paid off-cycle, coded to a special earning type, or run through a separate payroll. Those codes get left out of the deferral calculation when a system is first set up or changed.
1.3 Who is affected
Anyone with a percentage election who received a bonus in the affected period, plus anyone whose employer match or profit sharing depended on that pay. Highly compensated participants are often affected most, which also touches nondiscrimination testing.
2. How the Error Usually Starts
- A new payroll system or provider was configured without mapping every earning code to the plan definition.
- The plan was amended to change the compensation definition, and payroll was never updated.
- A new bonus program, commission plan, or retention payment was created with a new earning code.
- Different entities in a related group use different codes for the same pay type.
If this began after a system switch, review our guide on changing payroll providers, since the earning-code map is where these errors are born.
3. Confirm What the Plan Actually Requires
Before anyone moves money, establish the correct definition for each contribution type.
3.1 Pull the governing documents
Gather the adoption agreement, basic plan document, every amendment, and the current summary plan description. Confirm the versions in effect for each plan year at issue with your document provider.
3.2 Read the definition by contribution source
Compensation for deferrals, for the match, for profit sharing, and for testing can each be defined differently. Do not assume one definition applies across the board.
3.3 Check exclusions and special rules
Documents often exclude certain bonuses, such as sign-on or one-time awards, while including others. The exact wording matters, so read the language rather than relying on how payroll labels the pay.
3.4 Compare to the SPD and participant communications
If the SPD describes compensation differently than the document, document the discrepancy and take it up with your counsel and document provider. The operative document governs, but the mismatch affects how you correct and communicate.
4. Size the Error
You need a clear, reproducible calculation before any corrective deposit.
4.1 Build the affected population
Start from the recordkeeper roster and payroll history, not payroll alone. Include terminated participants who still hold balances, since they were shorted too.
4.2 Rebuild what should have been deferred
For each participant, apply their election percentage to the omitted bonus pay for the period. Note participants who changed or stopped elections during the period.
4.3 Recompute the match and other contributions
Missed deferrals can reduce the match. Rerun the match formula on the corrected deferral amounts and check any true-up provisions. Our post on the match true-up error covers that reconciliation.
4.4 Check limits and testing
Corrected deferrals can push a participant toward the annual limit or change test results. Review against the limits for your plan year and see excess deferrals and ADP/ACP test failures before depositing.
4.5 Decide what earnings to calculate
Corrections generally restore lost earnings as well. Agree on the method with your recordkeeper and document it.
5. Choose the Correction Path
Compensation errors are a recognized operational failure with established correction methods. Which one fits depends on how long the error ran, whether it is a plan-level pattern, and what the document says about the correction approach.
5.1 Self-correction where permitted
Many errors can be corrected without filing, provided you have established procedures and meet the conditions. Confirm eligibility with your advisor, as conditions depend on the facts and your plan year.
5.2 Compliance program filing when self-correction does not fit
If the error is not eligible for self-correction, a filing under the IRS compliance program may be needed. Review administrative error correction and the EPCRS framework for how sponsors approach this.
5.3 Fix the cause going forward
A correction without a configuration fix repeats next payroll. Update the earning-code map the same day you finalize the correction approach.
6. Self-Check: Eight Steps for Sponsors
- Identify the earning codes treated differently from the plan definition.
- Pull the document, amendments, and SPD for each affected plan year.
- Define compensation separately for deferrals, match, profit sharing, and testing.
- Build the affected roster from the recordkeeper, including terminated participants.
- Recalculate missed deferrals, match, and lost earnings with a documented method.
- Test the effect on annual limits and nondiscrimination results.
- Select and document the correction path with your advisor and recordkeeper.
- Fix payroll configuration, then test the next bonus run before it posts.
Fold this into your regular review using our year-end compliance calendar.
7. Where Sponsors Get Hurt
- Fixing only the current year and ignoring prior years the same error touched.
- Correcting deferrals but forgetting the match and lost earnings.
- Relying on the payroll provider’s description of the setup instead of reading the document.
- Leaving no written record of the calculation, decision, and approval.
- Not reconciling the participant data feed to the recordkeeper after the correction. See participant data reconciliation.
8. What You Can Delegate and What You Cannot
Payroll and the recordkeeper can run the numbers, map the earning codes, and post the corrective deposits. A third-party administrator can help with testing. But decisions that belong to the sponsor stay with the sponsor: whether to amend the compensation definition going forward, how to fund the correction, and how to communicate with affected participants. Those are settlor and fiduciary choices, and only the employer holds the facts about how bonuses are really paid. Review how roles divide in our post on 3(16) versus TPA services.
A 3(16) plan administrator takes on the day-to-day administrative duties, including monitoring that operations match the document, running reconciliations, and managing the correction process. That is the practical protection against a pay-definition error running unnoticed for plan years.
Put a Named Fiduciary Behind Your Plan
Most providers will not accept the ERISA 402(a) named-fiduciary appointment. Admin316 will. As your named fiduciary under 402(a) and your 3(16) administrator, we take responsibility for confirming that payroll follows the plan document, so a bonus coding gap does not turn into a multi-year correction. Book a call with Admin316 to review how your plan’s compensation definition is being applied.
