RSU withholding calculator: 22% withheld vs. what you owe
Employers withhold 22% on vesting RSUs whatever bracket you are in. If you are in the 32% bracket or higher, you owe the difference in April; this page sizes it and shows the per-paycheck fix.
Updated November 4, 2026 Sources and methodology
Federal income tax only. Payroll taxes are withheld separately and are not part of the shortfall shown above.
Flat rate or aggregate method
The IRS lets employers choose. Under the flat-rate method they withhold 22% of the vest (37% on the portion above $1 million of supplemental wages in the year). Under the aggregate method they treat the vest like an extra paycheck and apply your W-4 elections to it, which approximates your real bracket. Most large public companies use the flat rate because it is simple and because plans often default to sell-to-cover.
The result: the higher your bracket, the larger the gap. At a 24% marginal rate the shortfall is 2 points; at 35% it is 13 points; at 37% it is 15 points. On a $60,000 vest that is $7,800 of tax you owe in April on shares you may still hold.
How the shortfall is calculated here
- Federal tax on your total wages, minus federal tax on wages without the RSU, equals the tax the vest adds.
- Employer withholding = 22% of the vest (37% on supplemental wages above $1 million in the year, which this tool does not model because almost nobody reaches it).
- Shortfall = tax added − withholding. A negative number means you are overwithheld and will get it back.
- Per-paycheck fix = shortfall ÷ remaining paychecks, entered as extra withholding on line 4(c) of a new W-4.
The three ways to close the gap
| Method | When it works |
|---|---|
| Higher W-4 extra withholding | You have paychecks left and want it automatic |
| Quarterly estimated payment (Form 1040-ES) | You already passed a quarter, or you are self-employed too |
| Broker supplemental election | Your plan allows 37% or a custom rate |
Withholding is deemed paid evenly across the year, so a December W-4 change can still eliminate the penalty, though not the balance due.
Frequently asked
What percentage is withheld on RSUs in 2026?
A flat 22% federal, rising to 37% on supplemental wages above $1 million paid to the same employee in the calendar year (IRS Publication 15). Employers may instead use the aggregate method, which withholds as if the vest were a regular paycheck and often lands closer to your actual rate.
How do I avoid an underpayment penalty?
Pay at least 90% of your current-year tax liability, or 100% of last year’s (110% if prior-year AGI was above $150,000), through withholding or estimated payments. Withholding counts as paid evenly through the year, so increasing it in December still fixes the whole year.
Can I ask my broker to withhold more?
Some plans allow a supplemental rate election of 22% or a higher flat rate; a few allow a specific percentage. If yours does not, adjust your W-4 or make a quarterly estimated payment instead.
Sources. IRS Publication 15 (2026), section 7, supplemental wages; 2026 brackets from Rev. Proc. 2025-32. Estimates exclude payroll tax, additional Medicare tax, credits, and deductions other than the standard deduction.