Bonus Tax Calculator

Introduction

The cash from a bonus is often smaller than expected because payroll treats the payment as wages first and a planning event second. Before the employee sees the deposit, the gross amount can be reduced by federal supplemental wage withholding, Social Security and Medicare taxes, retirement or benefit elections, and any state or local withholding rule the employer applies.

U.S. payroll uses the term supplemental wages for pay that does not follow the usual salary or hourly paycheck pattern. Bonuses, commissions, overtime, severance, awards, prizes, back pay, taxable fringe benefits, and some tips can all fall into that category. The label matters because federal income-tax withholding can be calculated differently from a normal paycheck, even though the money is still part of taxable wages on the year-end return.

Withholding is also a timing rule, not the final tax answer. A paycheck can withhold too much or too little when compared with the employee's full tax return, because the return later combines all wages, filing status, deductions, credits, other income, and tax payments. That is why a bonus estimate should separate payroll cash flow from final tax liability.

Several payroll terms decide where the money goes:

Gross bonus

The announced bonus before tax withholding, retirement elections, payroll taxes, or other deductions.

Supplemental withholding

Federal income-tax withholding that can use a flat supplemental rate or an aggregate regular-pay calculation.

FICA wages

The wage base used for Social Security and Medicare taxes, which can differ from income-taxable wages.

Net bonus

The estimated take-home amount after modeled deferrals and withholding are subtracted.

Tax bases create many of the surprises. A pre-tax 401(k) election may reduce federal income-taxable wages, but it usually does not reduce Social Security or Medicare wages. Social Security withholding stops when the annual wage base is filled, Medicare continues with no wage base limit, and Additional Medicare withholding starts only after wages from the employer cross the federal withholding threshold.

The federal income-tax method can change the cash result even when the gross bonus stays the same. A separately identified bonus often uses a flat supplemental rate below the mandatory high-rate threshold. A bonus combined with regular wages can use an aggregate calculation that depends on regular taxable wages, pay frequency, filing status, and Form W-4 entries.

The practical limit is that a bonus estimate cannot know every employer payroll code or every state and local rule. Treat the result as a stated-assumption payroll estimate to check against pay-stub history, a verified state rate, current Form W-4 choices, and the year-end return that decides the final tax.

How to Use This Tool:

Start with the bonus amount, then add the payroll facts that change federal income withholding, FICA wages, and the state/local withholding base.

1. Enter Gross bonus as the bonus, commission, severance, or other supplemental wage amount before taxes, benefit elections, or deferrals.
2. Choose Federal withholding method. Pick Percentage method for a separately identified bonus that uses supplemental rates, or Aggregate method when the bonus is combined with regular wages for a Pub. 15-T payroll calculation.
   The method choice changes only the modeled federal income withholding. FICA and the state/local rate use their own bases.
3. Add Income-tax pre-tax bonus deferral if part of the bonus goes into a pre-tax election. Add Prior supplemental wages this year when the employee may approach the $1 million supplemental wage threshold.
4. For aggregate method planning, fill in Regular taxable wages this pay period, Pay frequency, and W-4 filing status. Open Advanced for Step 3 credits, Step 4(a) other income, Step 4(b) deductions, Step 4(c) extra withholding, the Step 2 checkbox schedule, or a known regular federal withholding amount.
5. Enter YTD FICA wages before bonus so the Social Security wage-base cap and Additional Medicare threshold can be modeled. If a deferral also reduces Social Security and Medicare wages, enter that portion as FICA-exempt part of deferral.
6. Add a verified State and local supplemental rate if one applies. In Advanced, leave state/local withholding applied after the income-tax deferral unless your jurisdiction or payroll setup taxes the gross bonus instead.
   If an error or warning names a negative dollar field, a rate outside 0% to 100%, or a capped deferral, correct that field before using the estimate.
7. Read Bonus Paycheck first for estimated take-home cash, then verify the same assumptions in Federal Method Comparison, Tax Line Ledger, Assumption Review, and Bonus Take-home Split.

Interpreting Results:

Estimated net bonus is the cash-planning result. Read it with the selected federal method, the take-home rate, and the warning list before treating the number as usable. A high take-home estimate may simply mean that the state/local rate is 0%, regular wages are missing in aggregate mode, or Social Security tax has already reached the wage base.

Federal Method Comparison explains the federal income-tax withholding difference. The percentage method applies supplemental wage rates to the income-taxable bonus. The aggregate method annualizes regular wages plus the below-threshold taxable bonus, subtracts regular federal withholding, and assigns the difference to the bonus.

Tax Line Ledger is the best place to verify the estimate. Check the federal income-tax base, FICA base, remaining Social Security wage-base room, Medicare lines, Additional Medicare line, and state/local base. The marginal-rate gap is only a planning comparison between withholding and a rate you enter; it does not predict the final refund or balance due.

Bonus Take-home Split converts the line items into a component chart. Use it to spot the deduction that moves the result most, then confirm the matching line in the ledger before changing a payroll assumption.

If a pay stub later shows a different number, compare pay frequency, regular taxable wages, federal method, year-to-date FICA wages, W-4 entries, deferral treatment, and state/local rate first. Remaining differences usually come from employer setup, local tax rules, benefit coding, per-line rounding, or wage history outside the estimate.

Technical Details:

Supplemental wage withholding separates payroll timing from final tax-return liability. Federal income-tax withholding on a bonus can use a flat supplemental wage rate, an aggregate calculation based on regular wages, or a mandatory high supplemental wage rate after cumulative supplemental wages for the employee exceed $1 million during the calendar year.

Net-bonus math works only when cash and taxable bases are kept separate. An income-tax pre-tax deferral reduces the income-taxable bonus and the cash available from the check. Social Security and Medicare use a separate FICA taxable bonus because many retirement deferrals reduce federal income-taxable wages without reducing FICA wages.

Formula Core

Two intermediate bases drive most of the result:

A simple substitution shows how the formula turns into a paycheck estimate. With a $15,000 bonus, a $1,500 income-tax deferral, $2,970 of federal supplemental withholding, $930 of Social Security tax, $217.50 of Medicare tax, no Additional Medicare tax, and $675 of state/local withholding, the estimated net bonus is $15,000 - $1,500 - $2,970 - $930 - $217.50 - $0 - $675 = $8,707.50.

Federal supplemental wage withholding is split before the selected federal method is applied. The part of the income-taxable bonus that keeps cumulative supplemental wages at or below $1 million can use the 22% percentage method or the aggregate method. Any excess over the $1 million threshold is modeled at 37% regardless of Form W-4.

For aggregate method calculations, period wages are annualized before the 2026 Pub. 15-T schedule is applied. The adjusted annual wage amount is:

The tentative annual withholding comes from the selected filing-status schedule and the standard or Form W-4 Step 2 checkbox schedule. W-4 Step 3 credits reduce tentative annual withholding but not below zero. The remaining annual amount is divided by pay periods per year, Step 4(c) extra withholding is added, and regular federal withholding is subtracted so only the bonus portion remains.

Displayed dollar amounts are rounded to cents for readability, while the component logic keeps the underlying tax lines separate until the final presentation. Small pay-stub differences can still appear because payroll systems may round each line, each period, or each jurisdiction differently.

Warnings identify assumptions that commonly change a bonus paycheck before the arithmetic is trustworthy:

Accuracy and Privacy Notes:

This is an educational payroll estimate for U.S. federal 2026 withholding assumptions. It is not tax, legal, financial, or payroll advice, and it does not decide final tax due on a return.

• State and local supplemental wage rules are not looked up. The state/local rate is the verified rate you enter.
• Employer payroll systems can differ because of benefit coding, rounding, payroll-period history, local taxes, and employee settings not represented by the exposed Form W-4 fields.
• Additional Medicare withholding uses the employer $200,000 withholding threshold, which can differ from the final filing-status liability thresholds on Form 8959.
• The estimate does not connect to a payroll account, tax account, or state tax database. If you share a changed page URL, check whether it contains private pay assumptions before sending it.

Advanced Tips:

• Use Regular federal withholding override when you have the actual regular-pay withholding from the same pay period. That keeps the aggregate method from relying only on the modeled regular paycheck.
• Keep Prior supplemental wages this year current for large bonus, commission, or severance years. Crossing the $1 million supplemental wage threshold changes the federal withholding rate on the excess portion.
• Enter FICA-exempt part of deferral only when the election actually reduces Social Security and Medicare wages. Most common pre-tax retirement elections reduce federal income-taxable wages but not FICA wages.
• Compare Federal Method Comparison before changing Form W-4 settings. The aggregate method can move sharply when regular taxable wages, pay frequency, Step 3 credits, Step 4 entries, or the Step 2 checkbox schedule changes.
• Use Tax Line Ledger before relying on the chart. The chart shows the split visually, but the ledger names the base and rate behind each withholding amount.
• Check the changed page URL before sharing a scenario because pay assumptions can travel with the link when you adjust the inputs.

Worked Examples:

A $15,000 bonus with a $1,500 income-tax pre-tax deferral, $92,000 in YTD FICA wages, a 5% state/local rate, and Percentage method selected leaves a $13,500 income-taxable bonus. Bonus Paycheck shows $2,970 of federal income tax withholding, $930 of Social Security tax, $217.50 of Medicare tax, $675 of state/local withholding, and about $8,707.50 as Estimated net bonus. Federal Method Comparison also shows that aggregate federal withholding would be about $4,183.70 with the default biweekly regular wages and single filing status.

A threshold case starts with $950,000 of prior supplemental wages and a new $120,000 bonus. Only $50,000 remains under the $1 million supplemental wage threshold, so Tax Line Ledger models $11,000 at the 22% supplemental rate and $25,900 at the 37% mandatory high supplemental rate. With $170,000 in YTD FICA wages, only $14,500 of the bonus remains subject to Social Security tax, and Additional Medicare withholding applies to $90,000 after the employer-paid wage total passes $200,000.

A troubleshooting example is a $5,000 bonus with a $4,800 income-tax deferral, aggregate method, no regular taxable wages, and a 20% state/local rate. The estimate can show negative net cash because the deferral, FICA taxes, and state/local withholding exceed the remaining cash. The warning list points to the zero regular taxable wages in aggregate mode and the negative net result, which are the first fields to check.

FAQ:

Glossary:

Supplemental wages

Wage payments outside regular wages, such as bonuses, commissions, severance, awards, or back pay.

Percentage method

The federal supplemental wage method that withholds 22% on eligible below-threshold supplemental wages.

Aggregate method

A method that combines regular wages and supplemental wages, calculates regular payroll withholding, then assigns the extra withholding to the bonus.

Income-taxable bonus

The gross bonus after income-tax pre-tax bonus deferral, used for federal income withholding and the default state/local base.

FICA

Federal payroll taxes for Social Security and Medicare on covered wages.

Social Security wage base

The annual wage ceiling for Social Security tax, set to $184,500 for 2026 in this estimate.

Additional Medicare tax

An extra 0.9% Medicare withholding amount modeled after employer-paid wages exceed $200,000 in the calendar year.

W-4 Step 2 checkbox

A Form W-4 setting that uses a different Pub. 15-T withholding schedule for the aggregate method.

References:

• Publication 15 (2026), Employer's Tax Guide, Internal Revenue Service, updated April 30, 2026.
• Publication 15-T (2026), Federal Income Tax Withholding Methods, Internal Revenue Service, updated April 30, 2026.
• Contribution and Benefit Base, Social Security Administration.
• Topic no. 751, Social Security and Medicare withholding rates, Internal Revenue Service, updated January 20, 2026.
• Topic no. 560, Additional Medicare tax, Internal Revenue Service, updated June 1, 2026.