What is Bonus Tax Calculator?
Free bonus tax calculator. Estimate take-home pay from a bonus — federal supplemental withholding, FICA, state — and the shortfall or refund vs your true marginal rate. No signup.
Bonus Tax runs entirely in your browser using JavaScript (browser). Your data never leaves your device.
Free Bonus Tax Calculator
Estimate your take-home pay from a bonus. The calculator applies the 2025 federal supplemental withholding rules (flat 22%, or 37% above $1M), Social Security, Medicare, Additional Medicare, and state withholding — then compares the flat rate against your true marginal rate to show whether you will owe more or get a refund at filing.
Your bonus
2025 ratese.g. California 10.23%, New York ~11.7%. No-income-tax states (TX, FL, WA, NV, SD, WY, AK, TN, NH) are 0%.
Most employers use the percentage method for one-off bonuses.
Bonuses already paid this year. The federal rate steps to 37% past $1M cumulative.
Try a scenario
Estimated take-home
$36,657
Cash in hand after withholding and any 401(k)/HSA deferrals.
Withholding vs your true rate
Your estimated true federal marginal rate is 32.0%; this bonus was withheld at 22.0%.
Likely shortfall at filing: about $5,000.
Estimated take-home
$36,657
True marginal rate 32.0% vs 22.0% withheld — ~$5,000 short at filing.
Take-home
$36,657
📐 Open methodology, sources & limitations
Formula
Federal-withholding base = bonus − 401(k) deferral − HSA contribution Percentage method: federal withheld = base × 22% (37% on the part above $1M YTD supplemental) Aggregate method: federal withheld ≈ base × true marginal rate FICA wage = bonus − HSA (401(k) deferrals remain FICA-taxable) Social Security = min(FICA wage, SS wage base − base salary) × 6.2% Medicare = FICA wage × 1.45% Additional Medicare = incremental wages above threshold × 0.9% State withheld = base × state supplemental rate Take-home = bonus − 401(k) − HSA − federal − SS − Medicare − add'l Medicare − state Shortfall / refund = (base × true marginal rate) − federal withheld
Assumptions
- 2025 federal supplemental withholding rate of 22%, rising to 37% on cumulative supplemental wages above $1,000,000 (IRC §3402(g)).
- 2025 FICA figures: Social Security wage base $176,100 at 6.2%, Medicare 1.45%, Additional Medicare 0.9% above $200,000 single / $250,000 MFJ.
- Base salary is used as a proxy for year-to-date wages when applying the Social Security wage cap and the Additional Medicare threshold.
- Traditional 401(k) deferrals reduce income-tax withholding but remain subject to FICA; HSA contributions made through payroll are exempt from both.
- The true marginal rate is read from the 2025 federal brackets at base salary plus bonus.
Sources
- IRC §3402(g) — Withholding on supplemental wages — §3402(g)
- IRS Publication 15 (Circular E) — Employer’s Tax Guide
- IRC §3101 — FICA Social Security and Medicare tax — §3101
- IRC §3101(b)(2) — Additional Medicare Tax — §3101(b)(2)
This tool does NOT model:
- The aggregate method is approximate — actual aggregate withholding depends on the pay period and your W-4
- State supplemental rate is entered manually — local income tax (NYC, Yonkers, Ohio municipalities) is not modeled
- Year-to-date wages are approximated from base salary, not entered directly
- Non-cash bonuses (stock, gift cards, prizes) and employer flat-rate elections above the supplemental rate
- Tax years other than 2025 — rates and the wage base adjust annually
Last reviewed: 2026-05-20 · Tax year modeled: 2025
This methodology section exists so you can verify the math. We show our formulas because you deserve to know how a number was calculated. This is calculation transparency, not financial advice.
Why so much of your bonus disappears
A bonus is a supplemental wage, and the IRS lets employers withhold federal income tax on it at a flat rate rather than running it through your W-4. Under the percentage method — which most employers use for a one-off bonus — that flat rate is 22% (and 37% on cumulative supplemental wages above $1M in a year). On top of that come Social Security, Medicare, the Additional Medicare surtax for high earners, and state withholding. It is normal for 35–45% of a bonus to be withheld before it reaches your account.
Withholding is not the same as the tax you owe. The 22% flat rate is a stand-in for your real marginal rate. If your true marginal bracket is 24%, 32%, or 35%, the 22% withholding leaves a shortfall you will settle at filing. If your marginal rate is 12%, the 22% rate over-withholds and the difference comes back as part of your refund. This calculator shows both the withholding and the gap.
Deferring the bonus into a 401(k)
Routing part of a bonus into a traditional 401(k) reduces the amount subject to federal (and usually state) income tax withholding — but not the amount subject to FICA. Social Security and Medicare are still withheld on the full bonus. HSA contributions made through payroll are the rare item exempt from both income tax and FICA.
Percentage vs aggregate withholding
- Percentage method. The bonus is treated separately and withheld at the flat 22% supplemental rate. Simple, predictable, and what most employers use for a discrete bonus payment.
- Aggregate method. The bonus is added to a regular paycheck and withheld as if that combined amount were your normal pay, using your W-4. This usually withholds closer to your true marginal rate — higher for high earners, lower for low earners.
- Crossing $1M. Once your cumulative supplemental wages for the year pass $1,000,000, the portion above that is withheld at the top 37% rate — a mandatory rule, not the employer's choice.
- Plan for the gap. If the calculator shows a shortfall, set the amount aside or increase your W-4 withholding so April is not a surprise. If it shows over-withholding, that money simply returns at filing.
- This is an estimate, not advice. Actual withholding depends on your employer's payroll system and your full-year picture. Confirm with a tax professional for large or unusual bonuses.
Frequently Asked Questions
Why is so much of my bonus withheld?+
A bonus is a supplemental wage. Most employers withhold federal income tax on it at a flat 22% under the percentage method, then add Social Security, Medicare, and state withholding on top. It is normal for 35–45% of a bonus to be withheld before it reaches you.
Will I get the extra withholding back?+
It depends on your true marginal rate. The 22% flat rate is a stand-in for your real rate. If your marginal bracket is below 22%, the bonus was over-withheld and the difference comes back as part of your refund. If it is above 22%, you will owe the shortfall at filing.
Should I defer my bonus into a 401(k)?+
Mechanically, routing part of a bonus into a traditional 401(k) reduces the amount subject to income-tax withholding (not FICA) and moves money into retirement savings. Whether that fits your situation depends on your goals and cash needs — this tool shows the mechanics, not a recommendation.
What is the difference between the aggregate and percentage methods?+
The percentage method withholds a flat 22% on the bonus treated separately. The aggregate method adds the bonus to a regular paycheck and withholds as if that combined amount were normal pay, using your W-4 — usually closer to your true marginal rate. Most employers use the percentage method for a one-off bonus.
What happens if my bonus pushes me over $1M for the year?+
Once cumulative supplemental wages for the year exceed $1,000,000, the portion above that is withheld at the top 37% federal rate. This is a mandatory rule, not the employer’s choice.
Why is my state withholding so high?+
Many states have their own supplemental withholding rate for bonuses — California uses 10.23%, New York around 11.7%. States with no income tax (Texas, Florida, Washington and others) withhold 0%. Enter your state’s supplemental rate to model it.
Can my employer use a different rate?+
Employers must use at least the 22% supplemental rate (or the aggregate method), and 37% applies above $1M. Some employers voluntarily withhold more. They cannot withhold less than the required amount.
How does a bonus affect my quarterly estimated taxes?+
If the flat withholding leaves a shortfall versus your true rate, you may need to cover the gap through a quarterly estimated payment or extra W-4 withholding to avoid an underpayment penalty.
Is a bonus taxed the same way as RSUs?+
Both a cash bonus and RSU vesting are supplemental wages subject to the same flat federal withholding rules. RSUs add the wrinkle that the income is the share value at vest, and the shares can then gain or lose value — see the RSU Tax Calculator for that case.
What if my bonus is paid in stock?+
A stock bonus is still taxed as supplemental wages at its fair market value when paid. This calculator models cash bonuses; the withholding mechanics are the same, but the value is the stock’s value at payment.
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