Bonus Tax Shortfall Calculator
Cash bonuses are taxed as supplemental wages — flat 22% federal withholding (37% above $1M YTD), regardless of your real bracket. If your marginal rate is 32% or higher, the gap shows up as a surprise bill at filing. Estimate yours below.
Tax year 2026 · Last updated May 11, 2026
mathstub / bonus shortfall
How much more do you owe on your bonus after April?
Cash bonuses are withheld at the 22% federal supplemental flat rate. For high earners in the 32–37% bracket, that withholding leaves a five-figure gap the IRS expects you to true up at filing — or earlier via quarterly estimates. (IRC § 3402(g)(1))
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Estimated shortfall on this bonus
$814 owed
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Suggested quarterly estimated payment
$0
Or extra W-4 withholding (~14 bi-weekly checks left)
$58.14 / paycheck
Show the math
How it works
- Enter your bonus amount. Type in the gross dollar value of the bonus (sign-on, performance, retention, year-end — anything paid as supplemental wages).
- Add your year-to-date wages. Include your regular W-2 wages and any prior supplemental wages (RSU vests, prior bonuses) paid earlier this year.
- Pick your filing status and state. These determine your federal marginal rate and whether state supplemental withholding applies.
- Read the shortfall and suggested action. If the shortfall exceeds $1,000, consider a quarterly estimated payment or extra W-4 withholding to avoid the IRS underpayment penalty.
Frequently asked questions
Why is my bonus only withheld at 22%?
IRC §3402(g) and IRS Pub 15 (Employer's Tax Guide) treat bonuses, RSU vests, and other supplemental wages as a single category. Reg. §31.3402(g)-1 sets a flat 22% federal withholding rate on the first $1,000,000 in YTD supplemental wages, then 37% on the excess. The 22% is a default the IRS chose — it is not your real marginal rate.
I got a $20,000 bonus and my employer withheld $4,400 (22%). Will I owe more in April?
Probably yes if your marginal federal rate is above 22%. For a single filer with W-2 wages of $200,000 + a $20,000 bonus in 2026, the marginal federal rate is 32% and California adds another ~10–12% — so the real federal+state liability on the bonus is closer to $8,400, not $4,400. The $4,000 gap is the shortfall.
What is the $1,000,000 threshold?
Per Reg. §31.3402(g)-1(a)(2), once your year-to-date supplemental wages with this employer cross $1M, every dollar above the threshold is withheld at 37% (the highest individual rate). A single big bonus that crosses the threshold gets a blended rate. The calculator handles this blending automatically.
Does this apply to sign-on bonuses, retention bonuses, performance bonuses?
Yes. All cash bonuses paid through W-2 payroll are "supplemental wages" under IRC §3402(g) and use the same 22%/37% withholding regime. The math is identical regardless of the bonus name.
What about clawbacks if I leave before the vesting date?
Clawback tax treatment depends on the year. If you repay in the same calendar year as the bonus, your W-2 is reduced and you net to zero. If you repay in a later year, you may be eligible for an IRC §1341 "claim of right" deduction or credit. This calculator estimates the year-of-payment tax only — clawback recovery is a separate filing-time question for your CPA.
Do I need to make estimated tax payments?
Maybe — especially if the shortfall is over $1,000 (the IRC §6654 safe-harbor threshold). The IRS rules in §6654(d) let you avoid an underpayment penalty by paying either 90% of this year's tax or 100% of last year's (110% if your prior-year AGI was above $150k). See IRS Publication 505 (Tax Withholding and Estimated Tax) for your situation, and the Mathstub Quarterly Estimated Tax calculator.
What if I am over-withheld (negative shortfall)?
A negative shortfall means you will get a refund on the bonus portion at filing time. This is common for lower-bracket filers (the 22% supplemental rate over-withholds for anyone whose marginal rate is 22% or below). The calculator labels this case clearly.
How does the "aggregate method" of withholding compare?
Some employers use the "aggregate method" (Reg. §31.3402(g)-1(a)(1)(ii)) — they treat the bonus as part of the next regular paycheck and withhold at your normal payroll-tax rate. This usually withholds MORE than the flat 22% method, so your shortfall is smaller. The calculator assumes the flat-rate method (the default for most large employers); if your employer uses the aggregate method, your real withholding will be higher than the calculator shows.
How accurate is the state tax estimate?
v1 uses each state's top marginal rate as an approximation. For users above the highest bracket the estimate is exact; for lower-income users it overstates state tax by a few percentage points. Use the override field to enter your exact rate.
Is this tax advice?
No — it is an estimate based on published IRS rules and your inputs. It does not consider AMT, multi-state residency, IRC §1341 claim-of-right scenarios, or other facts a CPA would catch. For decisions involving real money, talk to a licensed tax professional.
Spotted a bug, edge case, or numbers that look off? Tell us — we read every report.
