A $10,000 bonus with income tax withheld at 24% and 7.65% for Social Security and Medicare nets $6,835 — a 31.65% effective withholding. The number people report being shocked by is almost always this one, and the usual reaction is that the bonus was "taxed at 40%" or whatever the withholding happened to be.
bonus tax = bonus × applicable rate (marginal or flat supplemental), plus social security
Withholding is not the final tax. It is an estimate collected at source, and the annual return reconciles it. If too much was withheld the excess comes back as a refund; if too little, the balance is owed. The bonus is taxed at whatever rate your total annual income puts it in, and the withholding method has no effect on that.
A flat supplemental rate and your marginal rate rarely agree
Many payroll systems allow two approaches to supplemental pay. The flat method applies a fixed percentage — 22% in the US for supplemental wages under a threshold — regardless of your own bracket. The aggregate method adds the bonus to the regular pay period, computes withholding on the combined amount, and treats the annualised figure as your rate.
The aggregate method usually withholds more, sometimes far more, because one large period makes the payroll system behave as though you earned at that rate all year. Both reconcile at filing, but the cash flow differs sharply, and someone in a low bracket receiving a bonus under the aggregate method can be over-withheld by thousands for a year.
Deferral and pre-tax contributions; not the withholding method
Since the withholding method changes only timing, the levers that change the actual tax are the ordinary ones: directing part of the bonus into a pre-tax pension, deferring receipt into a year with lower income, or using it to fund a deductible contribution. Each reduces taxable income rather than merely delaying the collection.
Deferral is worth checking before assuming it helps. Moving income from a year in one band to a year in a higher band costs money, and in several systems deferred compensation carries its own rules and risks. The calculation is whether your marginal rate next year is genuinely lower, not whether the bonus feels large this year.
State and local withholding, caps, and the final reconciliation
Only one social contribution rate is applied, at a flat percentage. Most systems cap the social security portion at an annual ceiling, so a bonus received late in the year when the ceiling is already reached carries no further social withholding at all — a difference this calculation will not show.
State, provincial and local income tax withholding is outside the model entirely and can add several points. And the net figure here is what arrives, not what the bonus ultimately costs: only the annual return settles that.
Frequently Asked Questions
How is a bonus taxed?
A bonus is usually treated as income and taxed like other earnings, though some systems apply a flat supplemental withholding rate at payout. This calculator lets you choose either method and adds social-security withholding to estimate the net amount.
Why does my bonus seem taxed at a higher rate?
Flat supplemental withholding or stacking the bonus on top of your salary can push the withholding rate above what you expect. That is withholding, not necessarily your final tax — any excess is refunded when you file if your overall rate is lower.
Will I get some bonus tax back?
Possibly. If the amount withheld exceeds your actual tax on the bonus once your full year is assessed, the difference comes back as part of your refund. If too little was withheld, you may owe more at filing.
Does social security come out of a bonus?
In the US, yes: 6.2% Social Security until your wages for the year pass the wage base ($184,500 for 2026), and 1.45% Medicare on all of it. The calculator applies the rate you enter to the whole bonus, so enter 1.45% if you have already passed the wage base.
Are bonus tax rules the same everywhere?
No. Some countries have specific supplemental rates, others simply add the bonus to income, and social-security treatment varies. The defaults are the US rules — a 22% flat supplemental rate (37% above $1 million) or your marginal rate, plus 7.65% — so replace them for another country.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
The bonus is taxed at a single rate (marginal or flat supplemental) for illustration; real systems may stack the bonus on top of your other income.
Social-security withholding applies at the rate entered without a wage cap.
The defaults are 2026 US figures — the 22% flat supplemental rate or your marginal rate, and 7.65% for Social Security and Medicare; other countries and years differ, so verify them.
Results are estimates for general and educational use.
Where it stops
Supplemental withholding methods, flat rates, social-security caps, and final tax treatment vary by country and year — no figure here is authoritative.
Withholding at payout often differs from the final tax on the bonus, which is trued up at filing.
A flat supplemental rate can over-withhold for lower earners and under-withhold for higher earners.
This tool does not file a return or guarantee the net amount your payroll will actually pay.
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Tax rules vary by country, state, tax year, filing status, income type, deductions, and exemptions. This calculator is educational and uses the values you enter. Always verify final tax treatment with official sources or a qualified tax professional.
Published the calculator with its formula, worked example, assumptions, limitations and a bespoke guide, and added an automated formula test suite covering it.
Verified both withholding methods against each other, and documented that withholding is not the final tax — the annual return reconciles it.
Replaced the placeholder 6% social rate with the US 7.65% for Social Security and Medicare, so the $10,000 example nets $6,835 at a 24% marginal rate and $7,035 at the 22% flat supplemental rate.
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