RSU tax withholding calculator.

An RSU vest is a paycheck made of shares. The moment the shares vest, their market value is wages: your employer withholds federal income tax, Social Security and Medicare, and usually sells or holds back enough shares to pay it. This calculator shows those withholdings for 2026, using the federal supplemental-wage rules and the 2026 Social Security wage base, so you can see how many shares reach your account and whether the withholding will be enough.

How this is calculated

The vest value is shares times the price on the vest date. Publication 15 (2026) says federal income tax on supplemental wages paid separately from regular wages can be withheld at a flat 22% (no other percentage allowed) when the employer withheld income tax from your regular wages in the current or previous year. Once supplemental wages paid to you by that employer in the calendar year exceed $1 million, the excess is withheld at 37%, regardless of your Form W-4. The tool applies 22% to the part of the vest that fits under the $1 million line and 37% above it, using the prior supplemental wages you enter.

Social Security tax is 6.2% on wages up to the 2026 wage base of $184,500, so the tool applies it only to the room left after your year-to-date Social Security wages. Medicare is 1.45% on all of the vest. Publication 15 also requires employers to start withholding Additional Medicare Tax of 0.9% on wages above $200,000 in the calendar year, so the tool applies it to the part of the vest that crosses that line. State tax is simply your rate times the vest value. As of 2026-10-26, all of these figures come from Publication 15 (2026).

When the vest is taxed, Publication 525 says you include the fair market value of the property, minus anything you paid, in income for the year it becomes substantially vested, and your holding period starts then. So the vest-day price is your cost basis for the shares.

Worked examples (hypothetical figures, real rules)

A typical vest. 500 shares vest at $80, so the vest value is $40,000.00. You have $90,000 of Social Security and Medicare wages so far this year and have been paid no other supplemental wages. Federal withholding is 22% of $40,000, or $8,800.00. Social Security is 6.2%, or $2,480.00. Medicare is 1.45%, or $580.00. State at 5% is $2,000.00. Total withheld is $13,860.00 (34.6% of the vest), leaving $26,140.00 in shares and cash, about 326 shares if the plan sells 174 to cover. If your marginal federal rate is 32%, the flat 22% leaves roughly $4,000.00 of federal tax to be settled when you file.

A vest that crosses $1 million. You are paid $600,000 of supplemental wages before a $1,000,000 vest (10,000 shares at $100). Only $400,000 of the vest fits under the $1 million line, so 22% applies to that part ($88,000.00) and 37% to the remaining $600,000 ($222,000.00). Federal income tax withheld is $310,000.00. Your Social Security wages are already above the 2026 wage base of $184,500, so no more Social Security tax is withheld ($0.00). Additional Medicare Tax adds $9,000.00.

Mistakes people make

• Reading 22% as your tax rate. It is the rate your employer must use to withhold; your actual tax is worked out on your return at your real brackets.
• Forgetting FICA. Social Security and Medicare come out of the vest as well, which is why total withholding is well above 22%.
• Using the grant price. Tax follows the price on the vest date, not the price on the grant date.
• Taxing the sale twice. The vest-day value is your cost basis. Selling at that price produces no further gain.

Who this is for, and what it does not cover

It is built for employees of a company that pays RSUs through payroll. It does not cover stock options, ESPP shares (see the ESPP calculator), RSUs for non-employees, the Section 83(i) deferral election, double-trigger RSUs of private companies that vest on a liquidity event, local taxes, or states with unusual supplemental rates. Share counts and rounding are set by your employer and broker, so the payslip is the final word.

Sources

Retrieved 2026-10-26. Each link was opened and checked against the claim next to it.

• IRS Publication 15 (2026), Employer’s Tax Guide: section 7 supplemental wages (flat 22%, 37% above $1 million), the $184,500 social security wage base, 1.45% Medicare and the $200,000 Additional Medicare Tax withholding threshold.
• IRS Publication 525 (2025), Taxable and Nontaxable Income: restricted property: include fair market value minus any amount paid when it becomes substantially vested; holding period begins at vesting.