RSU withholding calculator
Employers withhold a flat 22% federal and 10.23% California on RSU vests and bonuses. If your marginal rate is higher, the difference is a bill in April — and below the safe-harbor floor, a penalty. A few numbers show the gap and the fix: per paycheck on your W-4 and DE-4, or a higher withholding rate on the vests still to come. Tax year 2026, California residents.
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Federal
- Tax on salary + RSUs
- Withheld at current settings
- April balance
- Safe-harbor floor
California
- Tax on salary + RSUs
- Withheld at current settings
- April balance
- Safe-harbor floor
Withholding counts as paid evenly through the year on Form 2210, so raising 4(c) now still clears installments you already missed. Penalty figures use the provisional 2026 rates (7% federal, 8% California).
What this assumes
Standard deduction, wages only, no credits. Your employer's regular-paycheck withholding is assumed to match the tax on your salary alone — true for a single-job household on a default W-4; two earners without Step 2 checked are usually short on salary too. RSUs are withheld at the 22% federal flat rate (37% on the part above $1M) and the 10.23% California rate. The California floor is 90% of this year's tax; federal uses the lesser of 90% of this year or 100% (110% over $150k AGI) of last year. The rate election on remaining vests is a federal lever only (California's 10.23% is fixed), needs an employer that offers it, and caps at 37%. Vests landing in the last pay periods of the year cannot be fixed on a W-4 at all — only by an estimated payment, which this page does not cover. Paychecks left are counted from your cadence and last pay date the way the app does it — stepping by actual pay dates, so a biweekly payday that lands in January is not counted; a year-end payday that falls on a weekend or holiday may be paid in the other year, so edit the count if yours does.
The app does the real thing: it reads your actual YTD withholding from paystubs, times each vest, includes prior-year facts, itemized deductions, capital gains, AMT, and computes the dated Form 2210 / FTB 5805 penalty exactly — then the per-paycheck number for both forms. On your computer; we never see it.