Safe Harbor 401(k) Plans: Mid-Year Suspension Rules and Costs

You can suspend safe harbor 401(k) contributions in the middle of a plan year, but only in narrow circumstances, and doing so pulls the plan back into the nondiscrimination testing it was designed to avoid. Federal regulations permit a mid-year suspension in two situations: the employer is operating at an economic loss for the plan year, or the annual safe harbor notice given to employees included language reserving the right to reduce or suspend contributions during the year.¹ If neither condition applies, you’re committed for the full year.

When a Mid-Year Suspension Is Allowed

The two gates are strict. An economic loss means a genuine operating loss for the plan year, not a cash-flow squeeze or a bad quarter. The alternative path is the notice reservation: if the annual safe harbor notice you sent employees before the plan year began stated that contributions could be reduced or suspended, you retain the option to do so.¹ Employers who didn’t include that reservation language when times were good often find themselves locked in when they need flexibility most.

One structural point worth flagging: employers using the 3% non-elective formula no longer send an annual safe harbor notice at all, because the SECURE Act eliminated that requirement for plan years beginning after December 31, 2019.² For those plans, the economic-loss condition is effectively the only route to a mid-year suspension.

The Suspension Process Step by Step

Once you’ve confirmed eligibility to suspend, the mechanics are prescribed and can’t be shortcut.

Amend the plan document. A formal amendment must be executed before the suspension takes effect, specifying the exact date employer contributions will stop.
Send a supplemental notice to every eligible employee. The notice must describe the suspension and its effective date, and the suspension cannot take effect until at least 30 days after employees receive it.¹
Give employees an election window. Participants must have a reasonable opportunity to change their deferral elections after receiving the supplemental notice and before the suspension takes effect. A 30-day election period is considered reasonable.³
Keep making safe harbor contributions through the effective date. The plan must operate under safe harbor rules for all compensation earned before the amendment takes effect, and those contributions remain fully vested.¹

The election window exists because employees may have been deferring at a higher rate specifically to capture the employer match. Once the match disappears, some will want to dial back their own contributions, and the regulations protect that right.

You Lose Safe Harbor Status for the Whole Year

This is the point that catches employers off guard. A suspension doesn’t just end the safe harbor prospectively; the plan loses safe harbor treatment for the entire plan year. That means the plan must pass the Actual Deferral Percentage and Actual Contribution Percentage tests covering all contributions made during the full year, using the current-year testing method.⁴

The ADP and ACP tests compare the average deferral and contribution rates of highly compensated employees to everyone else. For 2026, an employee is highly compensated if they earned more than $160,000 in the prior year.⁵ If the higher-paid group’s average rate outpaces the rest of the workforce by too wide a margin, the plan fails.

Top-Heavy Testing Comes Back Too

Safe harbor plans are normally exempt from being classified as top-heavy under Section 416 of the Internal Revenue Code.⁶ That exemption disappears along with your safe harbor status.

A plan is top-heavy if key employees, meaning owners and officers, hold more than 60% of the plan’s total account balances. A top-heavy plan must provide a minimum contribution of at least 3% of total compensation to every non-key employee employed on the last day of the year.⁷ For small businesses where owners hold most of the plan assets, this minimum can approach what you would have paid under the safe harbor formula in the first place.

What Failing the Tests Costs

If the plan fails the ADP or ACP tests, corrective options include refunding excess contributions (with earnings) to highly compensated employees or making additional qualified nonelective contributions to lower-paid employees to raise their average. Both routes are administratively disruptive and require calculations tied to each affected participant.

Failing the top-heavy rules means writing checks for the 3% minimum to every eligible non-key employee. For a plan with a meaningful gap in pay between owners and staff, the combined cost of testing corrections and top-heavy contributions can exceed what the suspension was meant to save. Run those numbers before you sign the amendment.

An Alternative: Retroactive Non-Elective Contribution

Employers sometimes suspend a safe harbor match, get through a hard year, and then face a failed ADP test the following spring. There is a way back into safe harbor status after the fact, but it only works for non-elective contributions, not matches, because a match depends on deferral decisions employees already made during the year.

3% non-elective, adopted late in the year. You can amend the plan to add safe harbor status with a 3% non-elective contribution up to 30 days before the end of the plan year.⁴
4% non-elective, adopted even later. If you increase the non-elective contribution to 4%, the amendment can be adopted any time before the last day of the following plan year.⁴

The extra percentage point is the price of the extended deadline. For an employer who suspended a match and is now looking at a failed ADP test with significant refund exposure, buying safe harbor status retroactively with a 3% or 4% non-elective contribution to the whole eligible workforce is sometimes cheaper than the correction alternatives.

Long-Term Part-Time Workers Count Too

When you assess who receives contributions before the suspension effective date and who has to be included in top-heavy or corrective contributions afterward, don’t forget the newer eligibility category. For plan years beginning after December 31, 2024, the SECURE 2.0 Act requires 401(k) plans to cover long-term part-time workers who log at least 500 hours in each of two consecutive 12-month periods and have reached age 21.⁸ Any of these employees who became eligible under your plan need to be treated consistently with other participants in your suspension analysis and in any post-suspension testing.

Before You Suspend

Confirm three things in this order. First, do you actually qualify to suspend, either through documented economic loss or through reservation language in your annual notice? Second, what does full-year ADP, ACP, and top-heavy testing look like based on year-to-date data? Third, would a retroactive non-elective contribution at the end of the year be cheaper than the corrections a failed test would force? A suspension that saves match dollars in the short run but triggers refunds, minimum contributions, and administrative rework can end up as the more expensive path.

1
eCFR. 26 CFR 1.401(k)-3 – Safe Harbor Requirements
2
Internal Revenue Service. Notice Requirement for a Safe Harbor 401(k) or 401(m) Plan
3
Internal Revenue Service. Mid-Year Changes to Safe Harbor Plans or Safe Harbor Notices
4
Internal Revenue Service. Mid-Year Changes to Safe Harbor 401(k) Plans and Notices
5
Internal Revenue Service. Notice 2025-67 – 2026 Amounts Relating to Retirement Plans and IRAs
6
Office of the Law Revision Counsel. 26 USC 416 – Special Rules for Top-Heavy Plans
7
Internal Revenue Service. Is My 401(k) Top-Heavy?
8
Internal Revenue Service. Notice 2024-73