NSO Tax Calculator — Non-Qualified Stock Options

Exercising an NSO triggers a W-2 ordinary income event equal to the bargain element: (FMV at exercise − Strike price) × Shares exercised. That income is subject to federal ordinary tax at your marginal rate, 6.2% Social Security tax up to the $176,100 2025 wage base, 1.45% Medicare tax (uncapped), and 0.9% additional Medicare tax once total wages cross $200,000 single / $250,000 MFJ. State income tax also applies in non-zero-tax states. The bargain shows on Box 1 of your W-2 with code V in Box 12.

Most employers withhold 22% federal income tax on NSO exercises (the supplemental wage rate up to $1 million; 37% above). If your true marginal rate at the NSO exercise level is 32%, 35%, or 37%, your employer is under-withholding by 10–15 percentage points × the bargain element. On a $300,000 NSO exercise that shortfall could be $30,000–$45,000 you need to pay at filing — or via a Q4 estimated tax payment to avoid underpayment penalties. Most NSO holders should run a tax projection at exercise time and either make an estimated payment or increase W-4 withholding for the rest of the year.

Once you exercise an NSO and hold the shares, your basis is the FMV at exercise (which equals strike + bargain). Any appreciation from the exercise FMV to the sale price is a capital gain — short-term ordinary rates if held under 1 year from exercise, long-term capital gain rates (0/15/20%) if held 1 year or more. NIIT 3.8% may apply above $200k single / $250k MFJ if you're in NII territory. There is no further FICA on the post-exercise gain — only the bargain at exercise was subject to payroll tax.

If a single-year NSO exercise would push your ordinary income into the 32%, 35%, or 37% bracket, spreading across two or more calendar years can save 5–7 percentage points × bargain on the portion that would have been taxed at the higher bracket. The Social Security wage base also matters — if your base salary already exceeds the wage base, additional NSO bargain isn't subject to 6.2% SS, but Medicare still applies. Run the calculator at different exercise sizes and compare net proceeds.

Yes — for NSOs that allow early exercise (vested or unvested), filing a Section 83(b) election within 30 days of the early exercise locks in the bargain element at the grant-equivalent FMV. If FMV = strike at early exercise, the bargain is zero and you have no W-2 ordinary income event at vest. All future appreciation becomes capital gain (long-term if held 1+ year from exercise). The risk: if you forfeit unvested shares or the stock drops below your basis, the cash you spent on the strike and any tax paid is not recoverable. Most useful at very early-stage startups.

A cashless or same-day exercise simultaneously exercises the NSO and sells the shares, using the sale proceeds to fund the strike price and tax withholding. You walk away with whatever cash is left after strike + tax. Tax-wise this is identical to a regular exercise + immediate sale: the bargain at exercise is ordinary income + FICA, and the tiny window between exercise FMV and sale FMV produces an even-tinier (often-zero) short-term capital gain. The benefit is you never need to put up cash — useful when the strike is high or the bargain is large.

NSOs trigger ordinary income + FICA at exercise on the bargain. ISOs trigger no regular tax at exercise but the bargain is an AMT preference, and if you hold 2 years from grant + 1 year from exercise the entire spread from strike to sale is long-term capital gain. NSOs are flexible (you control the timing), available to contractors and directors, and have predictable tax outcomes. ISOs are employees-only, capped at $100k first-exercisable per year, and require AMT planning. Use the ISO vs NSO calculator for a side-by-side comparison.