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RSU Tax Calculator: know exactly what you keep — before the vest date

Your company withholds a flat rate. Your real tax is bracket-based. The difference — the withholding gap — is how people end up owing five figures in April, or quietly overpaying their state all year. See both numbers now.

Assumes one W-2 employer, standard deduction, flat-rate supplemental withholding, and that this is your only RSU vest this year (multiple vests shift the $1M / Medicare / Social Security thresholds — the app version tracks them all). Tax year 2026 (federal official · CA brackets 2025 until FTB publishes 2026).

This bites real people every April

“We were very naive... did not do our due diligence to make sure the proper amount was being withheld and we got hit with an $80k bill (still pains me to think about).” — r/personalfinance
“The 22% is NOT enough if you have a large salary. It's just basic tax brackets at the end of the day.” — r/personalfinance
“Taxed on 300k and now only worth 180k, can't even sell to pay for due tax.” — Blind

RSU tax questions, answered straight

Why isn't the 22% withholding enough?

Federal law makes your employer withhold a flat 22% on RSU income (37% only above $1M cumulative). If your salary + vests put you in the 32–37% bracket, the flat rate under-collects — and the IRS expects the difference at filing. On a $150k vest that's routinely $10k–20k.

What is sell-to-cover, exactly?

Your broker sells part of the vesting shares to pay withholding and gives you the rest. The number of shares sold is set by flat withholding rates — not your actual tax — which is why a gap remains.

Why is my CA withholding higher than my real CA tax?

CA withholds a flat 10.23% on stock comp, but a large share of tech income sits in CA's 9.3% bracket. So CA often over-withholds while federal under-withholds. Opposite directions — this calculator shows each separately.

Do I need quarterly estimated taxes?

If your gap is big, yes — Apr 15 / Jun 15 / Sep 15 / Jan 15, or hit the safe harbor (110% of last year's tax if AGI > $150k) to avoid underpayment penalties.

Does Washington tax my RSUs?

No income tax on wages in WA — vests are federal-only. Selling later at a large long-term gain can trigger WA's separate 7–9.9% capital-gains excise tax.