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Why this happens
Large vests stack on top of salary and bonus, so the top dollars can fall in higher brackets than a flat rate assumes.
Additional wage-based taxes and investment-income surtaxes can apply at higher income levels, on top of tax.
Employer is calibrated to simple supplemental rules, not to your full household income.
The gap compounds when there are multiple vests, a working spouse, or other large income in the same year.
What to check
- Your estimated full-year income including all vests, bonuses, and household income.
- The flat rate used for vs. your likely .
- Whether higher-income surtaxes may apply to you this year.
- State adequacy, especially after a move.
- Whether estimated payments or extra is the cleaner fix for you.
Common mistake
Example scenario (hypothetical)
Illustration only, not your tax situation.
When to get help from a tax pro
- Equity is a large and growing share of your compensation.
- You may be subject to additional Medicare tax or net investment income tax.
- You have concentrated stock you are deciding when to diversify.
- You want a repeatable estimated-payment routine tied to your calendar.
Related calculators
Related pages
- RSUs and Marginal Tax Rates
RSU vest income stacks on salary. your marginal rate on that vest slice may be higher than flat withholding.
- RSUs and Net Investment Income Tax
NIIT generally applies to net investment income, not RSU wages at vest. but later sales and dividends can matter.
- RSUs and Medicare / Additional Medicare Tax
Large RSU vests can push wages over thresholds where additional Medicare tax may apply.
- RSU Tax Guide for High Earners
When RSUs are a large share of pay, withholding gaps and surtaxes deserve a deliberate plan.
For learning, not filing
Grants, employers, and states all differ. Use your own documents and a qualified tax professional before you make decisions from this guide.
