NSO Exercise History: Withholding Verification and Basis Tracking

Non-Qualified Stock Option exercises create ordinary income that should appear on your W-2. Verify that your employer withheld taxes correctly, confirm your cost basis is fair market value at exercise, and track capital gains when you eventually sell.

Ordinary income was recognized at exercise. The spread between the exercise price and the fair market value at the time of exercise is treated as ordinary compensation income. This amount should appear on your W-2 (if you are an employee) or 1099 (if a contractor). Your employer is required to withhold income tax, Social Security, and Medicare on this amount.

Verify your employer withheld correctly. Some payroll systems under-withhold on large NSO exercises, especially when the exercise happens late in the year or when supplemental wage withholding rates apply. If your employer withheld at the flat 22% supplemental rate but your marginal bracket is 32-37%, you could owe a significant balance at filing.

Your cost basis is FMV at exercise. When you eventually sell the shares, your basis is the fair market value on the date of exercise -- not the exercise price. Any gain or loss from that basis forward is capital gain or loss, subject to long-term or short-term treatment depending on how long you hold the shares after exercise.

The pitfall: The most common mistake is forgetting that basis resets to FMV at exercise. Reporting the wrong basis on your return can trigger an IRS notice and potentially double-count income already taxed through your W-2.