Nondiscrimination testing is a set of annual IRS checks that confirm an employer-sponsored benefit plan doesn’t tilt its tax advantages toward owners and highly paid employees at the expense of everyone else. The tests apply to 401(k) and other retirement plans, cafeteria plans, self-insured health plans, and several other tax-favored arrangements. When a plan fails, the fix ranges from writing refund checks to highly paid employees, to making extra contributions for rank-and-file workers, to paying excise taxes, to losing the plan’s qualified status entirely.
The logic behind the rules is straightforward. Federal law gives these plans favorable tax treatment because Congress wants employers to offer benefits broadly. Testing is how the IRS confirms the benefits actually reach the broad workforce.
Which Plans Have to Be Tested
More plan types are subject to testing than most employers assume.
- Traditional 401(k) plans must pass annual deferral and contribution tests. ERISA-governed 403(b) plans face similar requirements.
- Section 125 cafeteria plans, which let employees pay for health coverage and other benefits with pre-tax dollars, have their own rules. Benefits flowing to key employees cannot exceed 25 percent of the total nontaxable benefits the plan provides.
- Self-insured health plans must satisfy eligibility and benefits tests under IRC Section 105(h).
- Group-term life insurance plans providing more than $50,000 in coverage per employee are tested under IRC Section 79.
- Dependent care assistance programs under Section 129 also carry nondiscrimination requirements.
Retirement plans get the most attention, but a welfare plan failure can be just as expensive for the employees hit by it.
Who Counts as Highly Compensated or Key
Every test compares what higher-paid employees receive against what everyone else gets, so classifying the workforce correctly is the first step. Two categories drive the math.
Highly Compensated Employees
Under IRC Section 414(q), a Highly Compensated Employee (HCE) is anyone who owned more than 5 percent of the business at any point during the current or preceding year, or who earned more than $160,000 from the employer in the preceding year. The $160,000 figure applies for the 2026 plan year. An employer can optionally narrow the compensation-based group to the top-paid 20 percent of employees, but the 5-percent ownership test always applies with no such election.
Ownership attribution complicates this step. Under Section 318, stock owned by a spouse, child, grandchild, or parent is treated as owned by the employee, so an employee who personally holds no shares can still land in the HCE group through a family member’s ownership. Misclassifying even one person can flip a test from pass to fail.
Key Employees
Key Employees drive top-heavy testing and cafeteria plan testing. Under IRC Section 416(i), the category captures three groups: officers earning more than $235,000 in 2026, anyone owning more than 5 percent of the business, and anyone owning more than 1 percent while earning over $150,000. The officer compensation threshold adjusts annually for inflation.
Coverage Testing Under Section 410(b)
Before an employer reaches the deferral and contribution tests, the plan has to pass a minimum coverage test under IRC Section 410(b). The question is whether the plan covers enough non-highly-compensated employees relative to the HCEs it benefits. A plan satisfies coverage by meeting one of these standards:
- Percentage test: the plan benefits at least 70 percent of all non-highly-compensated employees.
- Ratio percentage test: the percentage of NHCEs who benefit is at least 70 percent of the percentage of HCEs who benefit.
- Average benefit test: the plan uses a classification the IRS considers nondiscriminatory, and the average benefit percentage for NHCEs is at least 70 percent of the average for HCEs.
A plan that fails coverage cannot be qualified, no matter how the other numbers come out. Employers with unionized and non-unionized workforces, multiple divisions, or an ESOP alongside a traditional 401(k) may have to disaggregate parts of the plan and test each portion separately.
The ADP and ACP Tests
When people talk about nondiscrimination testing for 401(k) plans, they usually mean the Actual Deferral Percentage (ADP) test and the Actual Contribution Percentage (ACP) test. The ADP test looks at employee elective deferrals. The ACP test looks at employer matching contributions and any after-tax employee contributions.
Both tests work the same way. The plan calculates the average deferral or contribution rate for the HCE group and compares it to the average for the NHCE group. The HCE average passes if it does not exceed the greater of:
- 125 percent of the NHCE average, or
- the lesser of 200 percent of the NHCE average, or the NHCE average plus 2 percentage points.
The practical result: the allowable gap between the two groups shrinks as NHCE participation drops. If NHCEs defer an average of 2 percent, HCEs can defer up to 4 percent. If NHCEs average 6 percent, HCEs can go up to 8 percent. In industries with high turnover or lower wages, NHCE participation stays low and the ceiling for HCEs stays tight. That’s where most failures happen.
For the 2026 plan year, the basic elective deferral limit is $24,500, so high earners are constrained first by the statutory cap and then by whatever the ADP test allows.
Top-Heavy Testing
The top-heavy test under IRC Section 416 looks at accumulated account balances instead of annual contribution rates. A plan is top-heavy when Key Employees hold more than 60 percent of all account balances as of the last day of the preceding plan year. This test catches plans that technically cover everyone but where nearly all the wealth inside sits in owner and officer accounts.
When a plan is top-heavy, the employer must make a minimum contribution of at least 3 percent of compensation for every non-key participant, or match the lower HCE contribution rate if that is less. These contributions vest under an accelerated schedule. Many small businesses will trigger top-heavy status almost by default because the owner’s balance dwarfs everyone else’s, making the required minimum an annual budget line.
Testing for Cafeteria and Self-Insured Health Plans
Welfare benefit plans have their own regimes with different mechanics and different consequences.
Section 125 Cafeteria Plans
Cafeteria plans have to pass three tests. The eligibility test ensures the plan does not favor highly compensated individuals in who can participate. The contributions and benefits test checks that HCEs do not receive a disproportionate share of the plan’s tax-free benefits. The key employee concentration test caps benefits flowing to key employees at no more than 25 percent of the total nontaxable benefits provided under the plan. If any of the three tests fail, the penalty lands only on the favored group: HCEs and key employees lose pre-tax treatment and must include the value of their benefits in gross income. Rank-and-file employees keep their tax-free status.
Section 105(h) Self-Insured Health Plans
Self-insured medical plans face an eligibility test and a benefits test. The eligibility test is satisfied if the plan benefits at least 70 percent of all employees, or if at least 70 percent of employees are eligible and at least 80 percent of those eligible actually benefit. The benefits test requires that every benefit available to highly compensated individuals also be available to everyone else. Different deductibles, waiting periods, or covered services between groups will fail the test.
When a self-insured plan fails, the highly compensated individuals must include any “excess reimbursements” in gross income. Unlike a retirement plan failure, this is a targeted tax hit rather than a threat to the plan’s status.
Safe Harbor: The Way to Skip ADP and ACP Testing
Employers who want to avoid the annual ADP and ACP testing exercise can adopt a Safe Harbor 401(k) design. Safe Harbor plans are treated as automatically passing the deferral and contribution tests because the employer commits upfront to a minimum contribution for all eligible employees. The cost is real: the employer funds contributions regardless of whether individual employees participate.
Three standard Safe Harbor formulas satisfy the requirement:
- Non-elective contribution: the employer contributes at least 3 percent of each eligible employee’s compensation, whether or not the employee defers anything.
- Basic match: the employer matches 100 percent of the first 3 percent of compensation the employee defers, plus 50 percent of the next 2 percent, for a maximum employer contribution of 4 percent.
- Enhanced match: any matching formula at least as generous as the basic match, such as dollar-for-dollar on the first 4 percent deferred.
Safe Harbor contributions must vest immediately, or within two years for certain QACA designs. The employer also has to deliver a written notice to eligible employees 30 to 90 days before each plan year begins. Missing the notice window or failing to fund the required contributions can retroactively strip Safe Harbor status and leave the plan subject to standard ADP and ACP testing. Plans consisting solely of Safe Harbor contributions are also exempt from top-heavy testing.
Fixing a Failed Test
A failed ADP or ACP test is not unusual, and the correction procedures are well-established. Speed is what matters.
Employers have two primary options:
- Corrective distributions: return excess contributions and their allocable earnings to the HCEs whose deferrals pushed the average too high. These refunds are taxable to the HCE in the year distributed and are reported on Form 1099-R.
- Qualified Non-Elective Contributions (QNECs): the employer makes additional contributions to NHCE accounts to raise their average until the plan passes. QNECs vest immediately.
If corrective distributions go out within 2½ months after the plan year ends, the employer avoids the 10 percent excise tax on excess contributions under IRC Section 4979. Plans using an eligible automatic contribution arrangement get a longer six-month window. Miss those deadlines and the excise tax applies on top of the required correction.
If the failure is still uncorrected 12 months after the plan year ends, the cash-or-deferred arrangement is no longer qualified and the entire plan is at risk. At that point, returning money to HCEs alone is not enough, QNECs to NHCEs become mandatory, and the employer will typically need to use the IRS’s Employee Plans Compliance Resolution System (EPCRS). EPCRS offers three tracks depending on how the mistake was found: self-correction for operational failures the employer catches on its own, voluntary correction with a user fee for more serious or older failures, and audit closing agreements for problems the IRS discovers first. Sanctions climb sharply as the correction moves from the first track to the third.
When a Plan Loses Qualified Status
Disqualification is the ceiling outcome, rare but severe. When a plan loses its qualified status, the plan trust itself loses its tax exemption and has to file its own income tax return and pay tax on investment earnings. Employees must include any vested employer contributions made during the years of disqualification in their taxable income. And the employer loses the ability to deduct contributions when made; deductions are delayed until the contributions become taxable to employees.
For a small business owner who has been funding a plan for years, disqualification can unravel the entire tax strategy the plan was built on. That is what gives the testing deadlines their weight. The math is mechanical. The stakes behind it are not.