What is a safe harbor 401(k)?

The problem safe harbor solves

A regular 401(k) plan has to prove it does not favor highly compensated employees. It does this with two annual tests named in the publication: the ADP test, which compares the deferral percentages of higher-paid and lower-paid employees, and the ACP test, which looks at employee and matching contributions. If the tests fail, the employer may owe a 10% excise tax on the excess contributions, reported on Form 5330, and a plan that fails and does not fix it by the end of the next plan year can be disqualified. For a small business whose owners want to defer a lot, that risk is real.

The safe harbor 401(k) trades certainty for cost. If you meet the safe harbor requirements, you do not have to satisfy the ADP test or, if certain additional requirements are met, the ACP test.

The two employer formulas

The publication states the conditions. Matching contributions: 100% of each non-highly compensated employee’s elective deferrals up to 3% of compensation, plus 50% of deferrals from 3% up to 5% of compensation. The match rate for highly compensated employees, including the owner, cannot exceed the rates for the non-highly compensated. Nonelective contributions: at least 3% of compensation for all non-highly compensated employees eligible to participate, whether or not they defer.

Either way, the mandatory contributions must be immediately 100% vested and are subject to special withdrawal restrictions. You must give eligible employees a written notice of their rights and obligations within a reasonable period before the plan year; that notice requirement does not apply when you make nonelective contributions and either make no matching contributions or make matches intended only to satisfy the ACP test. All the other 401(k) rules, including withdrawal and vesting rules, must also be met.

Worked example

An employee earns $60,000 and defers 5% ($3,000). Under the basic match the employer contributes 100% of the first 3% ($1,800) and 50% of the next 2% ($600), for $2,400, which is 4% of pay. If the employee defers only 3%, the match is $1,800. If the employee defers nothing, the match is zero. Under the 3% nonelective alternative the employer contributes $1,800 regardless of whether the employee defers. The calculator above shows both, using the plan compensation limit for the year.

Which is cheaper depends on participation. If most employees defer 5% or more, the nonelective formula costs less (3% against 4% of pay). If few employees defer, the match costs less.

The top-heavy rules, and why safe harbor avoids them

Publication 560 explains that a top-heavy plan is one that mainly favors partners, sole proprietors and other key employees. A plan is top-heavy for a plan year if, for the preceding plan year, the total value of accrued benefits or account balances of key employees is more than 60% of the total for all employees. Additional requirements then apply, primarily to provide minimum benefits or contributions for non-key employees. Most qualified plans must contain provisions that take effect in years when they are top-heavy (section 416).

The relief: the top-heavy requirements do not apply to SIMPLE 401(k) plans, to safe harbor 401(k) plans that consist solely of safe harbor contributions, or to qualified automatic contribution arrangements. In the calculator, enter key-employee and total balances to see the 60% test: for example, $450,000 held by key employees out of $700,000 total is about 64.3%, so the plan is top-heavy; $380,000 out of $700,000 is 54.3%, so it is not.

QACA, a cousin of the safe harbor

The publication describes a qualified automatic contribution arrangement (QACA) as a type of safe harbor plan. It adds automatic enrollment, with a default deferral that must be uniform, no more than 15% after 2019, at least 3% in the first plan year and rising to at least 6% in later years, and mandatory employer contributions, a match of 100% of the first 1% and 50% from 1% to 6%, or nonelective contributions of at least 3%. Its employer contributions must be 100% vested after 2 years of service. Plans created on or after December 29, 2022 generally must include automatic enrollment unless an exception applies, effective for plan years beginning after 2024.

Limits that still apply

A safe harbor plan still has the usual limits. The elective deferral limit is $23,500 for 2025 and $24,500 for 2026, with a catch-up of $7,500 for 2025 and $8,000 for 2026 for participants 50 or older, and a higher catch-up of $11,250 at ages 60 to 63. Annual additions to an account are capped at the lesser of 100% of compensation or $70,000 for 2025 ($72,000 for 2026). Compare the SIMPLE alternative on our SIMPLE IRA match page, and see our 401(k) contribution limit calculator for the deferral side.

Sources

• IRS Publication 560, Retirement Plans for Small Business (SEP, SIMPLE, and Qualified Plans) (2025): Chapter 4: Qualification Rules (Top-heavy plan requirements; SIMPLE and safe harbor 401(k) plan exception); Elective Deferrals (401(k) Plans); Treatment of Excess Deferrals (Tax on excess contributions of highly compensated employees); Safe Harbor 401(k) Plan; Qualified automatic contribution arrangement (QACA). Read November 2, 2026.

Edition read: Publication 560 (2025), for use in preparing 2025 returns. Where the publication gives 2026 figures, this page labels them 2026. Dollar limits change every year; check the current publication and form instructions for your plan year. This page summarizes the publication and does not replace it.