Estimates only — not financial, tax, or professional advice.
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What it calculates: Net bonus, Total tax withheld, Income tax, Effective withholding rate.
Updated 5 June 2026 · Transparent assumptions
30% withheld, and the withholding is not the tax
A $10,000 bonus with income tax withheld at 24% and 6% of social contributions nets $7,000 — a 30% 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.
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.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
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.
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