Calculator
RSU Withholding Estimator
Your employer withholds a flat 22% on RSUs because the IRS tells it to, not because that's your tax rate. If your income lands in the 32% or 35% bracket, every vested dollar is short by a tenth or more — and it never shows up on a paystub. This works out what the vest actually costs, what withholding rate would have covered it, and the extra 0.9% Medicare that two-earner couples get caught by.
Uses published 2026 federal figures
What the vest costs · 2026
Enter what's vesting and the rest of your year, then press Calculate.
Your vesting shares
The total market value of everything vesting this calendar year, at the price on each vest date. That whole amount is wages — it lands on your W-2 whether or not you sell a single share.
The supplemental rate is what payroll withholds. It is 22% by default because the IRS says so, and it has nothing to do with your bracket. Anything past $1,000,000 of supplemental pay in one year is withheld at 37% automatically.
Market value on the vest dates, before any shares are sold to cover
22% unless payroll was asked to change it
Deduction
The rest of your year
Your salary and cash bonus, excluding anything that vests, and the federal income tax withheld from them. Your last payslip of the year has both; earlier in the year, annualize the year-to-date figures.
A spouse's wages go in separately because their employer applies its own thresholds. That separation is what surfaces the extra 0.9% Medicare gap, which no single payroll department can see.
Interest, short-term gains
Quarterly payments you've sent in yourself
State
Two flat rates you supply, rather than a fifty-state bracket table. A built-in table would be a maintenance liability that goes stale silently, and a stale table is worse than an honest input — the shortfall arithmetic is the same either way.
Many states withhold supplemental wages at a fixed rate that sits below their own top bracket, which is the same trap as the federal 22%, one layer down. Leave both at 0% if your state has no income tax.
What this income actually costs
What payroll withholds on the vest
Both are optional. Filling them in adds a state line to the results and to the PDF; leaving them at zero simply omits it.
Last year, for the safe harbor
Owing money in April is not itself a penalty. The penalty only applies if you paid in less than the smaller of 90% of this year's tax and 100% of last year's — 110% if last year's AGI was over $150,000.
In a year when a big vest lands, last year's figure is usually far cheaper to match. Both are on line 24 and line 11 of your prior return. Leave them at zero and only the 90% test is used, which is the stricter assumption.
Form 1040, line 24
Form 1040, line 11
For educational purposes only. Results are estimates and do not constitute financial, tax, or legal advice. Consult a qualified professional before making any financial decisions.
How to use it
Put in the total market value of everything vesting this year — the price on each vest date, before any shares are sold to cover. That entire amount is wages, whether or not you sell.
Then add your salary and the federal tax withheld from it. Both are on your last payslip of the year; earlier than that, annualize the year-to-date figures and the answer scales with them.
The headline is a rate, not a dollar figure, because the rate is the thing you can act on — it's what you take to payroll. Most companies let you set a higher supplemental withholding rate, and some let you do it per vest.
Press Example to load a worked case: a $200,000 salary with $150,000 vesting, which is close to the scenario that comes up most often.
Why 22% is the wrong number
22% is a withholding rate set by regulation for supplemental wages. It is not an estimate of your tax rate and was never meant to be one. Payroll applies it because it is told to, not because it knows anything about your return.
Vested shares land on top of your salary, so they occupy the highest brackets your income reaches. Somebody whose salary already fills the 24% bracket has a vest taxed at 32% and 35% while a flat 22% is withheld — a gap of ten points or more, on every dollar, invisible until April.
Above $1,000,000 of supplemental pay in one calendar year the excess is withheld at 37% automatically, which is the one case where the default is roughly right.
The 0.9% nobody withholds
There is a second, quieter gap. An extra 0.9% of Medicare tax applies to wages above $200,000 for a single filer and $250,000 for a couple filing jointly.
But an employer is required to start withholding it once it has paid one employee more than $200,000 — regardless of filing status, and with no knowledge of a spouse.
Two people earning $150,000 each owe the surtax on $50,000 of combined wages, and neither employer withholds a cent of it. The tool prices that gap separately from the RSU shortfall, because they are two different problems with two different fixes.
Assumptions and limits
- Brackets and the standard deduction are the published 2026 figures from IRS Rev. Proc. 2025-32; the flat supplemental rate is from Publication 15. Both change annually.
- The recommended rate covers federal income tax on the vest and nothing else, because that is all a supplemental withholding rate does. The Medicare surtax is withheld through a different mechanism and is reported separately.
- The vest is assumed to come from the same employer as your salary — the usual case, and the conservative one for the Medicare calculation.
- State tax is two flat rates you supply. A built-in fifty-state table would go stale silently between updates, and a stale table is worse than an honest input.
- Not modeled: the alternative minimum tax, tax credits, incentive stock options, ESPP disqualifying dispositions, share rounding on sell-to-cover, or a vest that straddles a calendar year boundary.
- An estimate for planning. Not tax advice, and not a substitute for someone looking at your actual return.