What does this RSU vest actually cost you?

Tax year 2026 · updated
You
Salary plus any bonuses and other vests for the whole year. Sets which brackets this vest lands in.
Year-to-date pay before the vest date. Determines how much Social Security and Additional Medicare the employer withholds from this paycheck.
Only matters once cumulative supplemental pay passes $1,000,000, when withholding jumps to 37%.
Interest, short-term gains, side income. Not spouse wages (entered above).
The vest
22% is the default flat rate. Change it only if your employer lets you elect a higher one.
Blank assumes your employer withholds at your state marginal rate. Enter your state's supplemental rate if you know it.
Annual payment target (optional)
Form 1040, line 24.
Form 1040, line 11.
Tax this vest creates
—
— of —
Employer withholds
—
— of the vest
Still owed at filing
—
negative means over-withheld

Where the numbers come from

TaxOwedWithheldGap
Total

Shares

Vested
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Sold to cover withholding
—
Left in your account
—
More to set aside for the gap
—

Your inputs stay on this page. Sharing creates a link that carries them.

Methodology

How the vest is taxed

RSUs are ordinary wage income on the vest date, measured at fair market value (IRC §83; Reg. §1.83-1). The tool prices the vest as the top slice of your year: federal and state income tax with the vest minus the same tax without it, using the standard deduction and the 2026 rate schedules from Rev. Proc. 2025-32. FICA follows IRC §3101: Social Security at 6.2% up to the $184,500 wage base, Medicare at 1.45% with no cap, and the 0.9% Additional Medicare tax above $200,000 single / $250,000 joint / $125,000 separate.

Why withholding misses

Employers withhold federal tax on RSUs at the flat supplemental rate of 22% (37% once your cumulative supplemental wages for the year exceed $1,000,000) under Reg. §31.3402(g)-1. That rate has nothing to do with your actual bracket. Anyone whose income with the vest lands in the 24% bracket or above is under-withheld on the federal side. Employers also withhold the 0.9% Additional Medicare only on their own wages above $200,000, regardless of filing status or a spouse's income, which creates a second mismatch on joint returns.

Assumptions and limits
  • Standard deduction only; itemizing, credits, AMT, and the net investment income tax are not modeled.
  • Social Security and Additional Medicare withholding follow the employer's year-to-date wages at the vest date (Publication 15). With one employer, Social Security withheld now is tax owed; later wages above the wage base aren't taxed. Additional Medicare liability is computed on full-year household wages.
  • State tax uses the published schedule for single or joint filers; head-of-household and separate filers use the single schedule. Full deduction and exemption amounts are applied with no phaseouts.
  • State withholding is assumed to match your state marginal rate unless you enter your employer's supplemental rate. Local tax uses a statewide average and is assumed withheld.
  • The annual payment target follows IRC §6654(d): the lower of 90% of this year's tax or 100% of last year's (110% if last year's AGI exceeded $150,000, or $75,000 if married filing separately). It is a target, not a penalty determination: the IRS tests each installment period separately, and the tool doesn't know what has actually been withheld or paid.
  • Selling shares to cover tax creates a small capital gain or loss on any price movement after vest; the tool ignores it.
specifics not modeled