RSU Tax Calculator — your 22% withholding gap
Your company withholds RSUs at a flat 22%. You're probably in a higher bracket. See exactly how much more you owe — and the precise quarterly payment to make now so the IRS doesn't penalize you.
After your company withholds 22%, you'll owe
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Set aside now
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✅ Pay this now to avoid an IRS penalty
Sell-to-cover ≠ paid in full
⚠ Don't get taxed twice when you sell
Owe a surprise bill?
The RSU withholding gap, explained
When your Restricted Stock Units vest, the fair-market value of the shares is added to your W-2 as ordinary wage income. The IRS classifies that as supplemental wages, and it requires your employer to withhold federal tax at a flat 22% — or 37% on any supplemental wages above $1,000,000 in a calendar year. That flat rate is an administrative convenience, not an accurate measurement of your tax. If your salary plus your RSU income lands you in the 32%, 35%, or 37% marginal bracket — as it does for most tech and finance employees with meaningful equity — then 22% withholding leaves you 10 to 15 percentage points short on every vest. On a $200,000 vest, that gap alone can exceed $30,000.
Most calculators stop at "you might owe more." This one does three things they don't. First, it computes your true marginal liability using the full 2026 federal brackets, your state's rates, the Social Security wage base, and the 0.9% Additional Medicare Tax — then subtracts what was actually withheld to show the exact gap. Second, it tells you the quarterly estimated-tax amount to pay now under the IRS safe-harbor rules, with the deadline and a link to IRS Direct Pay, so you avoid the Form 2210 underpayment penalty. Third, it warns you about the cost-basis double-tax trap — the single most expensive mistake RSU holders make at sale.
Sell-to-cover doesn't settle the bill
About 70% of companies use "sell-to-cover": at vest they automatically sell enough shares to remit the mandatory withholding. It feels like the tax is handled. It isn't. Sell-to-cover only covers the flat 22% — the gap between that and your real marginal rate is still yours to pay. The calculator shows the shares sold, the shares you keep, and the amount you still owe after the sale.
The $0 cost-basis trap
When you eventually sell vested shares, your broker often reports a $0 cost basis on Form 1099-B. If you (or your tax software) file it as-is, you pay capital-gains tax on the entire sale proceeds — money already taxed as wages at vest. The fix is one line: on Form 8949, use Code B and enter your real basis (the FMV at vest) from your broker's supplemental statement. Read the full walkthrough in our cost-basis double-tax guide.
State-specific calculators: California, New York, Texas, Washington. More in the RSU tax guides.
RSU tax FAQ
Why do I owe more tax on my RSUs than my company withheld?
Employers are required to withhold federal tax on RSU vest income at the flat 22% supplemental rate (37% on supplemental wages over $1M in a year). But if your total income puts you in the 32%, 35%, or 37% bracket, 22% is far short of what you actually owe. The difference — the withholding gap — is yours to pay at filing or via quarterly estimated taxes.
How much should I set aside after an RSU vest?
Run your vest through the calculator above. The "Set aside now" figure is the exact amount your withholding fell short by, across federal, state, Social Security, Medicare, and the 0.9% Additional Medicare Tax. Hold that in cash and pay it with your next quarterly estimated payment.
Does sell-to-cover pay my full RSU tax bill?
No. Sell-to-cover sells just enough shares to remit the flat 22% withholding. Your true liability at your marginal rate is higher, so a gap remains even after sell-to-cover. The calculator shows the shares sold and the amount you still owe.
My 1099-B shows $0 cost basis on my RSU sale. Is that right?
No — that is the #1 RSU filing mistake and it double-taxes you. Your real cost basis is the fair-market value at vest (already taxed as W-2 income). When you sell, correct the basis on Form 8949 using Code B, taken from your broker’s supplemental statement. See our cost-basis guide.
Do RSUs trigger the 3.8% NIIT or AMT?
No. RSU vest income is wages, not investment income, so NIIT (3.8%) does not apply at vest — only to later capital gains if you hold and sell at a profit above the MAGI threshold. AMT applies to incentive stock options (ISOs), not RSUs.
Is this calculator private?
Yes. It runs entirely in your browser — your salary, share price, and RSU figures are never sent to any server. You can verify this in your browser’s DevTools Network tab.