The Actual Deferral Percentage test is the nondiscrimination check that decides whether a 401(k) plan is quietly tilting toward the highest earners. The IRS wrote it into Section 401(k) of the tax code to prevent plans from becoming tax shelters for executives while rank-and-file employees barely participate. Every plan that isn't a safe harbor plan has to run the ADP test annually, usually in the first quarter after year-end, and a failure means the employer has to return contributions to HCEs or make additional contributions to NHCEs within a tight correction window. For plan sponsors, the test is an annual audit of whether the plan actually works the way the law intends.
How the ADP Test Is Calculated The test runs in two steps. First, calculate each employee's deferral percentage: the percentage of eligible compensation they contributed to the 401(k), including elective deferrals and (for the ACP test, a related calculation) employer matching contributions. Second, average those percentages separately for HCEs and NHCEs.
An employee is an HCE if they owned more than 5% of the company in the current or prior year, or if they earned above the IRS compensation threshold ($160,000 for 2026 based on 2025 earnings). Everyone else is an NHCE.
What Are the ADP Test Pass Thresholds? The plan passes if the HCE average deferral rate is within a narrow band of the NHCE rate. If the NHCE rate is 0-2%, the HCE rate cannot exceed 2x the NHCE rate. If the NHCE rate is 2-8%, the HCE rate cannot exceed the NHCE rate plus 2 percentage points. Above 8% NHCE, the HCE rate cannot exceed 1.25x the NHCE rate. In practice, most plans fail (if they fail) when NHCE deferrals are low.
What Happens When a Plan Fails the ADP Test A failed ADP test has to be corrected by the plan's correction deadline (generally 2.5 months after plan year-end for the 10% excise tax avoidance window, 12 months for the correction to remain within qualified plan rules). Three correction options are available.
The first is corrective distributions: refund excess contributions (plus earnings) to HCEs, which is the most common fix but creates a taxable event for the affected executives. The second is qualified non-elective contributions (QNECs): the employer makes additional contributions to NHCEs to raise their average and close the gap. The third is a one-to-one correction: combining refunds and QNECs to balance the test. See the IRS ADP Fix-It Guide for the current procedural specifics.
Why Safe Harbor Plans Skip the ADP Test A safe harbor 401(k) plan trades a fixed employer contribution for automatic ADP test compliance. The employer agrees to either a non-elective contribution of at least 3% of compensation for all eligible employees, or a matching contribution that matches 100% of the first 3% of employee deferrals plus 50% of the next 2%. In exchange, the plan is exempt from the ADP test (and the related ACP test on matching contributions).
For plans with low NHCE participation, safe harbor is usually the cleanest option. It also simplifies HCE participation: executives can defer up to the annual 402(g) limit without worrying that a failed test will force a refund. Plans have to formally elect safe harbor status before the start of the plan year, with specific notice and funding requirements.
Building an Actual Deferral Percentage Test Strategy That Holds Up Three operational practices reduce the risk of a late-stage ADP test failure. First, run preliminary testing mid-year. Data is already in the plan's recordkeeping system; waiting until January to discover a problem limits the correction options. Second, watch NHCE participation trends. A falling NHCE deferral rate is the single strongest predictor of an ADP test failure.
Third, review the HCE/NHCE classification every year, especially after organizational changes. A reclassification error (treating an HCE as an NHCE or vice versa) can create a test failure on its own and expose the plan to additional IRS scrutiny. Plan sponsors that pair annual testing with formal documentation of each correction decision build a defensible record if the plan is ever audited by the IRS or DOL.
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