Should 401(k) Be Deducted From Your Bonus Check?

In most cases, yes — letting your standard 401(k) deferral come out of your bonus check is the right call, because the pre-tax contribution reduces your immediate income tax withholding and adds to your retirement savings. But the answer to whether a 401(k) should be deducted from a bonus check depends on three things: how close that deduction pushes you to the annual contribution limit, whether your employer’s match includes a year-end true-up, and whether you’d rather have the cash now. The 2026 elective deferral limit is $24,500, and a single large bonus can eat a surprising chunk of that room.¹

Why the Deduction Happens Automatically

Your plan document contains a formal definition of “eligible compensation” that determines what your deferral percentage applies to. Most plans define it broadly enough to cover discretionary bonuses, performance incentives, and commissions.² When a bonus fits that definition, your employer is required to apply your deferral election to it. Not deducting it would be a plan administration error.

The surprise is the dollar size. A 6% deferral on a $2,000 paycheck is $120. The same 6% on a $30,000 bonus is $1,800 pulled from one check. The percentage didn’t change; the base did.

What the Deduction Does to Your Take-Home Pay

The IRS treats bonuses as “supplemental wages,” along with commissions, overtime, and severance.³ Most employers withhold federal income tax on supplemental wages using the flat percentage method: 22% up to $1 million per year, 37% on anything above that in a single calendar year.⁴ The alternative aggregate method lumps the bonus with a regular paycheck and often withholds more.

A pre-tax 401(k) contribution lowers the amount of the bonus subject to income tax withholding. On a $20,000 bonus with a 10% deferral, withholding applies to $18,000, which saves you $440 in immediate federal withholding at the 22% rate. Many states follow the same logic for their own supplemental withholding.

FICA is different. Social Security and Medicare tax apply to the full bonus regardless of your 401(k) contribution, because pre-tax deferrals don’t reduce FICA wages.⁵ Social Security tax stops once your yearly earnings pass the wage base of $184,500 in 2026; Medicare has no cap.⁶

Roth deferrals behave differently on a bonus. A pre-tax contribution comes out after FICA but before income tax, giving an immediate tax break. A Roth contribution comes out after both.⁷ A $3,000 pre-tax deferral from a bonus reduces current withholding by about $660 at the flat rate. A $3,000 Roth deferral costs you the full $3,000 out of net pay now, with the tax-free treatment coming later in retirement.

The Front-Loading Trap and Lost Matching

Here’s where the default deduction can genuinely cost you money. If a bonus deferral pushes your year-to-date contributions near $24,500, your payroll system will stop all elective deferrals once you hit that ceiling.¹ That matters because many employer matches are calculated per pay period, not per year. A common formula is 50% of the first 6% you contribute each paycheck. If your contributions stop in September, you earn no match from October through December, and that money is gone for the plan year.

A quick example. You earn $100,000 with a $25,000 bonus paid in March. Your deferral rate is 15% and your employer matches 50% of the first 6%. A single March paycheck generates a $3,750 bonus deferral on top of the usual $625. You hit $24,500 well before year-end and lose several months of match.

Does Your Plan Have a True-Up?

Some plans include a true-up: a year-end reconciliation that recalculates your match based on total annual compensation and total annual deferrals. If the per-period calculation shorted you, the employer adds the difference. If your plan has a true-up, you can let the full bonus deduction run without losing match dollars.

If your plan does not have a true-up, pace yourself. Take $24,500, subtract what you’ve already deferred this year, and divide what’s left by the pay periods remaining. That’s your safe per-check ceiling. If letting the normal percentage come out of the bonus would blow past that pace, lower the percentage for the bonus pay period and raise it back afterward. The summary plan description or your benefits administrator will tell you whether a true-up exists, and the answer is worth asking about.

Changing Your Election Before the Bonus

You aren’t locked into whatever your default rate does. Most plans let you change your contribution percentage, and many allow per-pay-period changes. Two strategies cover most situations. To keep more cash, drop the deferral to 0% for the bonus period and reset it afterward. To accelerate savings, raise it, sometimes up to the remaining room under the annual limit. Many payroll systems cap the deduction at $24,500 automatically, but confirm with your administrator rather than assume.

Timing is the catch. Federal rules require your deferral election to be in place before the compensation is currently available to you.⁸ If your bonus pays January 30, your election must be on file before January 30. You can’t receive the bonus and then decide retroactively. Payroll processing deadlines usually run several business days ahead of the pay date, so a late change doesn’t just delay the switch; the bonus will process at your old rate with no fix after the fact.

When Deferring More From a Bonus Makes Sense

If you’re 50 or older, the 2026 catch-up contribution is $8,000, raising your total limit to $32,500. Participants between 60 and 63 get a larger catch-up of $11,250 under SECURE 2.0, for a total of $35,750.¹ A bonus is the easiest way to fill that extra room if you’ve been contributing below the cap through the year. Temporarily increasing your deferral for the bonus pay period captures the tax-advantaged savings without squeezing your regular paychecks.

One scheduling note for high earners: beginning in 2027, participants whose prior-year wages exceeded a specified threshold will be required to make catch-up contributions on a Roth basis only. That rule does not apply to 2026, but it’s worth knowing before you plan a multi-year bonus-deferral strategy.⁹

Extra Caution for Highly Compensated Employees

If you earned more than $160,000 from your employer in the prior year, the IRS considers you a highly compensated employee for plan testing.¹⁰ Your plan runs annual nondiscrimination tests comparing HCE deferral rates against everyone else’s. When HCEs funnel large bonuses into the plan, the gap can widen enough to fail the test.¹¹

This happens most often when someone changes jobs mid-year. Each employer’s payroll only sees its own contributions, so neither notices the combined total approaching the limit. The IRS treats aggregation across all your plans for the year as your responsibility.¹⁴ If you got a bonus at either employer this year, run the numbers before December 31.

1
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
2
Internal Revenue Service. 401(k) Plan Fix-It Guide – You Didn’t Use the Plan Definition of Compensation Correctly for All Deferrals and Allocations
3
eCFR. 26 CFR 31.3402(g)-1 – Supplemental Wage Payments
4
Internal Revenue Service. Employer’s Tax Guide (Publication 15)
5
Internal Revenue Service. Retirement Plan FAQs Regarding Contributions – Are Retirement Plan Contributions Subject to Withholding for FICA, Medicare or Federal Income Tax?
6
Social Security Administration. What Is the Current Maximum Amount of Taxable Earnings for Social Security?
7
Internal Revenue Service. Roth Account in Your Retirement Plan
8
eCFR. 26 CFR 1.401(k)-1 – Certain Cash or Deferred Arrangements
9
Internal Revenue Service. Treasury, IRS Issue Final Regulations on New Roth Catch-Up Rule, Other SECURE 2.0 Act Provisions
10
Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Cost-of-Living
11
Internal Revenue Service. Consequences to a Participant Who Makes Excess Deferrals to a 401(k) Plan
13
Internal Revenue Service. 401(k) Plan Fix-It Guide – Elective Deferrals Weren’t Limited to the Amounts Under IRC Section 402(g) for the Calendar Year and Excesses Weren’t Distributed
14
Internal Revenue Service. Retirement Topics – 401(k) and Profit-Sharing Plan Contribution Limits