Free tool
RSU Withholding Shortfall Calculator
Your employer withholds federal tax on RSU vests at a flat 22% — but a big vest can push you into a 32–37% marginal bracket. The difference is a shortfall you owe at filing, plus a possible penalty. Estimate the exact dollar gap below so you know how much cash to set aside.
Your situation
Estimate only — not financial or tax advice. Consult a qualified CPA before making decisions about setting aside cash, selling equity, or other financial moves.
Your RSU withholding gap
- Federal supplemental withholding (22% / 37%)
- $44,000
- Real federal tax on RSU income (marginal)
- $66,400
- State supplemental withholding
- $20,460
- FICA on RSU income
- $4,700
- Est. underpayment penalty
- $1,454
- Total owed at tax time (shortfall + penalty)
- $22,222
Based on tax year 2026 federal brackets, FICA, and state tables. The shortfall is your real marginal-bracket liability on the RSU income minus what your employer withholds (flat 22% federal supplemental, plus state supplemental and FICA).
Read the deep dive: Why RSU withholding falls short
RSU withholding shortfall FAQ
Why is RSU withholding usually too low?
RSU vesting is a supplemental wage. Employers withhold federal tax on supplemental wages at a flat 22% up to $1 million per calendar year, and 37% above $1 million (IRS Publication 15). If your salary plus RSU income puts you in a 32–37% marginal federal bracket, the flat 22% withholding leaves a shortfall you owe when you file — on top of any state shortfall.
How big is the RSU tax shortfall?
It depends on your bracket. The gap is roughly (your marginal rate − 22%) of your RSU income for the federal piece, plus any state shortfall. A high earner with $200,000 of RSU income in a 35% bracket can owe tens of thousands at filing. This tool estimates the exact dollar figure from your salary, vest value, filing status, and state.
Will I owe an underpayment penalty?
Possibly. If your total shortfall is $1,000 or more and you did not pay enough through withholding or estimated payments, the IRS can charge an underpayment penalty (IRS Form 2210). This tool includes a simplified penalty estimate; the actual figure depends on quarterly timing and safe-harbor rules, so confirm with a CPA.
Does this include FICA and state tax?
Yes. It estimates Social Security (6.2% up to the annual wage base), Medicare (1.45% plus the 0.9% Additional Medicare Tax on high earners), and state tax for CA, NY, IL, MA, NJ, OR (with WA and TX at 0%). For other states you can enter your own marginal rate and we flag it as an estimate to verify with a CPA.
Is this a substitute for tax advice?
No. This is a free estimate based on tax-year 2025 brackets and rates. It does not account for deductions, credits, AMT interaction, or your complete situation. Consult a qualified CPA before making decisions about selling equity or setting aside cash.
Want the full vest-by-vest picture across the year, with quarterly estimated-payment planning? Try the full RSU Tax Calculator.