401(k) Nondiscrimination Testing
Tax benefits cannot disproportionately favor owners and highly compensated employees. Testing converts plan terms, ownership, compensation, eligibility, and contribution data into an annual compliance result.
Reviewed July 29, 2026 · Source-led practitioner reference
Core tests
| Test | What it evaluates |
|---|---|
| Coverage under Code §410(b) | Whether enough nonhighly compensated employees benefit relative to highly compensated employees |
| ADP | Average elective-deferral rates of HCEs compared with NHCEs |
| ACP | Average matching and applicable after-tax contribution rates |
| Top-heavy | Whether key employees hold more than 60% of plan benefits, potentially triggering minimum contributions |
| Annual additions and deferrals | Whether participant and plan limits were exceeded |
Safe harbor does not mean test-free
A qualifying safe-harbor design can satisfy ADP and, when requirements are met, ACP testing. The plan still needs correct eligibility, compensation, contributions, notices where applicable, coverage, limits, related-employer analysis, and operational compliance. Additional contributions can also affect top-heavy treatment.
Data that changes the answer
- Ownership and family attribution.
- Controlled-group and affiliated-service-group membership.
- All eligible employees, including eligible noncontributors and terminees.
- The plan’s compensation definition and accurate payroll components.
- HCE, key-employee, and top-paid-group elections.
- Contribution sources, refunds, forfeitures, and prior corrections.
Failure response
Depending on the test and timing, correction may involve refunds, recharacterization, qualified nonelective contributions, additional employer contributions, or an IRS correction program. The sponsor should identify the root data or process failure rather than treating the calculation as a once-a-year vendor exercise.
Turn reference knowledge into working confidence.
Use this public guide for quick orientation and source review. Inside PrepToPay Benefits, you can study the topic in structured lessons, practice applying it, review flashcards, and track your progress across the broader Benefits curriculum.
Primary sources
- IRS — ADP and ACP nondiscrimination Fix-It Guide
- IRS — Is my 401(k) top-heavy?
- IRS — Operating a 401(k) plan
Educational reference only. Plan documents, governing law, agency guidance, and plan-specific professional advice control.
Keep building your retirement-plan operations system.
Finally, place every vendor, fee, investment, contribution, and operational decision inside a documented fiduciary process.