Bonus withholding calculator

A bonus is taxed like the rest of your pay, but it is usually withheld differently, which is why the deposit can look like it was taxed at 40%. This estimates the withholding when your employer uses the flat-rate method for supplemental wages — federal income tax, Social Security, Medicare, and optional 401(k) and state lines — and the likely deposit. It estimates withholding, not your final tax, and it is not tax advice. Nothing you type leaves your browser.

Bonus withholding estimator

Likely take-home from the bonus—

Federal income tax (flat 22% / 37%)—
Social Security (6.2%)—
Medicare (1.45% + 0.9%)—
State—
401(k)—
Withheld overall—

Estimates withholding when your employer uses the optional flat-rate method for supplemental wages: 22% federal, and a mandatory 37% on supplemental pay above $1 million in a year (IRS Publication 15 (2026), Employer's Tax Guide). Social Security 6.2% up to the 2026 wage base of $184,500 (SSA — Contribution and benefit base); Medicare 1.45% plus 0.9% on wages over $200,000 (IRS Topic 751 — Social Security and Medicare withholding rates). Some employers use the aggregate method instead, which can withhold more or less. Withholding is not your final tax — the difference is settled when you file. Your state's rules and rate vary; enter your state's supplemental rate if you know it.

How the math works

Federal income tax: 22% of the bonus after any pre-tax 401(k) deferral, the optional flat rate for supplemental wages in IRS Publication 15. Supplemental pay above $1 million in a calendar year is withheld at a mandatory 37%, which is why the calculator asks about other bonuses already paid this year.
Social Security: 6.2% of the full bonus, but only on wages up to the 2026 wage base of $184,500 — a bonus paid after your wages for the year pass it has less, or none, taken out.
Medicare: 1.45% of the full bonus, plus the 0.9% Additional Medicare Tax on the part of your wages for the year above $200,000.
401(k) and state: the 401(k) percentage comes off before the federal and state lines, not before Social Security and Medicare. The state line applies the rate you enter; each state sets its own supplemental method and rate, and some have no wage income tax.
Your employer may use the aggregate method instead — adding the bonus to a regular paycheck and withholding as if that were your normal pay — which can take out more or less than this.
Withholding is a prepayment, not your tax bill. On your return the bonus is taxed like the rest of your wages, so if your top bracket is above or below 22%, the difference shows up as a balance due or a refund when you file.

Educational information about careers and earning — not financial, investment, legal, tax, or individualized career advice. Read the full disclaimer.

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