Executive Summary
How do I adjust my W-4 for equity compensation?
You can add extra withholding on Form W-4 to cover the shortfall from RSUs and stock options. Use Line 4(c) to withhold an additional dollar amount per paycheck. Or use Line 4(a) to enter other income (like expected RSU vesting) so the IRS calculates higher withholding. Either way, you avoid a surprise tax bill at filing time. The 22% supplemental rate on RSUs often isn't enough—extra withholding fills the gap.
Your RSUs vest. Your employer withholds 22%. You're in the 32% bracket. That's a 10% shortfall—and it adds up. A $50,000 vesting means $5,000 less withheld than you owe. You can fix that by adjusting your W-4.
The bottom line: Form W-4 lets you add extra withholding. Instead of making estimated payments, you can have more taken from your paycheck. It's automatic—no quarterly deadlines to remember. See our withholding guide for why the gap exists.
Why 22% Isn't Enough
| Your Bracket | Withholding on RSUs | Shortfall |
|---|---|---|
| 22% | 22% | 0% |
| 32% | 22% | 10% |
| 35% | 22% | 13% |
| 37% | 22% | 15% |
RSU vesting and NSO exercises use the supplemental rate. Your employer doesn't use your W-4 for that—they use a flat rate. So your W-4 only affects your regular salary. To cover the shortfall, you add extra withholding on the W-4.
How to Adjust
Option 1: Line 4(c) — Extra Withholding
Add a dollar amount per paycheck. Simple.
Example: You expect $30,000 in RSU vesting. You're in the 32% bracket. Shortfall = 10% of $30,000 = $3,000. If you get 24 paychecks, that's $125 per paycheck. Put $125 on Line 4(c).
Option 2: Line 4(a) — Other Income
Enter income you expect that won't have withholding. The form will increase your withholding to account for it.
Example: You expect $50,000 in RSU vesting. Put $50,000 on Line 4(a). Your employer will withhold more from your salary to cover the extra tax.
When to Update
| When | Action |
|---|---|
| Start of year | Set withholding for expected vesting |
| After big vesting | You might have over-withheld—you can reduce |
| Before vesting | Add extra if you know a big vest is coming |
| Job change | New employer = new W-4 |
ISO Exercise: No Withholding
For ISO exercises, there's no withholding at all—you owe AMT. The W-4 won't help with that directly. The extra withholding on your regular salary can help cover the AMT bill—but you may still need estimated payments. See our AMT guide.
Use the IRS Estimator
The IRS Tax Withholding Estimator lets you input your income, including expected equity compensation. It tells you if you're on track and suggests W-4 adjustments. Run it once or twice a year.
Frequently Asked Questions
Will my employer know I have equity?
They already know—they're the one granting it. The W-4 is between you and the IRS. Your employer just uses it to calculate withholding. They don't need to know why you're adding extra.
Can I reduce withholding mid-year if I overpaid?
Yes. Submit a new W-4 with lower withholding. You can adjust anytime. Just be careful not to under-withhold—you might owe at filing.
What about state tax?
State W-4 (or equivalent) works differently. Some states have their own forms. Check your state's tax agency. You may need to add extra state withholding too.
Disclaimer: This guide is for educational purposes. It does not constitute tax advice.
Last Updated: March 2026 | Research Team: VestingStrategy