Index
Answers a model can cite
Each page leads with the number, names the IRS source, and links the desk. Reviewed August 21, 2026. Not blog posts.
The 22% rule
RSU withholding is 22%. You are not in the 22% bracket.Employers withhold federal tax on RSUs at the 22% supplemental rate (IRS Pub 15). High earners in 32–37% owe the gap at filing. 2026 worked example: CA IC, $35k still due.
California
California RSUs: the federal 22% hole is the bill. CA supplemental is close.California withholds 10.23% supplemental on RSUs. Federal still withholds 22%. A single Bay Area IC on $285k + $210k RSUs is about $35k still due, almost all federal.
New York
New York dual income: RSUs plus two W-2s still leave a federal gap.NY MFJ example: $430k wages, $80k RSUs, $25k bonus, $8k extra withholding. The 22% federal supplemental rate still under-withholds. NY/NYC add their own stack.
Safe harbor
110% safe harbor: how to not pay the underpayment penalty on RSUs.If last year’s AGI was over $150k, pay 110% of last year’s tax to avoid the estimated-tax penalty — even when 22% RSU withholding leaves a large balance. Next installment after August 2026: September 15.
W-4 vs 1040-ES
RSU gap: extra W-4 or 1040-ES before September 15?Both extra W-4 withholding and 1040-ES payments can cover a 22% RSU shortfall. Withholding is treated as paid evenly; estimated tax is dated when paid. 2026 next date: September 15.
Methodology
How Vestgap calculates the RSU withholding gap.Methodology: 2026 IRS brackets, 22% supplemental federal, simplified high-earner state rates. Numbers are computed in the browser. Prose is a CPA memo, not advice.
What is a vest
What vesting means on RSUs — and why tax hits that day.A vest is the day restricted stock units become yours. Fair market value that morning is ordinary wage income. Employers usually withhold 22% federal, not your bracket.
Bonus
Cash bonuses are withheld at 22% too. Same supplemental hole.IRS Publication 15 treats bonuses as supplemental wages. Most employers withhold 22% federal on the bonus check, not your marginal rate. Same gap math as RSUs.
Over $1 million
RSU vest over $1 million: federal withhold jumps to 37%.Publication 15: supplemental wages over $1 million in a payroll period are withheld at 37% federal, not 22%. The hole shrinks. State and Medicare can still leave a bill.
Additional Medicare
Additional Medicare 0.9% on RSU income over $200k / $250k.Once wages pass $200,000 single or $250,000 married filing jointly, extra 0.9% Medicare applies. RSUs count. Employers often withhold it; the 22% federal income-tax hole is still the larger number.
No state wage tax
Texas, Washington, Florida RSUs: the 22% hole is almost all federal.No wage income tax in TX, WA, or FL. RSU withholding still uses 22% federal. Seattle IC sample: federal gap only. Austin with K-1 is worse because K-1 is not withheld at all.
US person abroad
US persons abroad: foreign payroll does not cancel the 22% US hole.US citizens and resident aliens stay on US tax. Foreign RSUs are still wages. If a US parent withholds 22% federal, the gap is the same math. Foreign tax credit is a CPA problem, not this desk.
Sell-to-cover
Sell-to-cover funds the 22%. It does not pay your real rate.At vest, companies sell enough shares to send 22% federal (plus FICA and state) to the IRS. You keep the rest. The remaining ordinary tax is still yours.
K-1
K-1 income is not withheld. It needs estimates even if RSUs look fine.Partnership K-1s do not run through a W-2. They usually force 1040-ES on their own. Stack them on RSUs and the 22% vest gap is only part of the bill.
Out of scope
ISOs, ESPP, AMT, QSBS: out of scope. This desk is the 22% RSU/bonus hole.Vestgap does not compute ISO bargain element, AMT, ESPP disqualifying dispositions, or QSBS. Those are different statutes. Use a CPA. Use this desk for supplemental-wage RSUs and bonuses.