Stock Options Tax Calculator

Stock options tax liability depends critically on the option type: Incentive Stock Options (ISOs) and Non-Qualified Stock Options (NSOs/NQSOs) are taxed very differently. Getting this wrong is one of the most common and costly tax mistakes in compensation planning.

NSO (Non-Qualified Stock Option) tax at exercise: Ordinary Income = (Fair Market Value at Exercise − Strike Price) × Shares Exercised Tax Owed = Ordinary Income × Marginal Income Tax Rate

ISO (Incentive Stock Option) tax at exercise:

• No regular income tax at exercise
• The spread (FMV − Strike Price) may trigger Alternative Minimum Tax (AMT)
• AMT Preference Item = (FMV at Exercise − Strike Price) × Shares

Capital gains tax on sale (both types): Capital Gain = (Sale Price − Tax Basis) × Shares Sold

Where:

• Strike Price (also called exercise price), price at which you can buy the shares, set at grant date
• Fair Market Value (FMV): current market price at time of exercise
• Tax Basis for NSOs: FMV at exercise (the income already taxed)
• Tax Basis for ISOs: strike price (for regular tax) or FMV at exercise (for AMT)
• Short-term capital gains: held < 1 year: taxed as ordinary income (up to 37%)
• Long-term capital gains: held > 1 year: taxed at 0%, 15%, or 20%

What makes an ISO disposition “qualifying”, which is the whole game: You must hold the shares two years from the grant date and one year from the exercise date, both. Clear both and the entire gain from strike price to sale price is long-term capital gain. Miss either and it is a disqualifying disposition: the exercise spread becomes ordinary income in the year you sell, and only the rest is capital gain. A same-day exercise-and-sell is always disqualifying, which is why an ISO sold immediately is taxed no better than an NSO.

Worked example, NSO: Strike $10, fair market value at exercise $40, 1,000 shares, 32% bracket.

• Ordinary income at exercise: ($40 − $10) × 1,000 = $30,000
• Federal income tax: $30,000 × 32% = $9,600
• Payroll tax: 7.65% if you are below the Social Security wage base, so $2,295. Above it, only the 1.45% Medicare applies and it drops to $435.
• Total at exercise: $11,895, on shares you have not sold

Sell two years later at $60. Your basis is the $40 already taxed, so the further $20 per share is a long-term gain: $20,000 at 15% = $3,000 more.

Worked example, ISO, same numbers:

• At exercise: no regular income tax at all. The $30,000 spread is an AMT preference item.
• Whether AMT actually costs you anything depends on the exemption, which is roughly $90,000 single or $140,000 joint for 2026. A $30,000 preference on its own is comfortably inside it, so most people exercising at this scale owe no AMT. Exercise 10,000 shares instead and the picture changes entirely.
• Sell at $60 after clearing both holding periods: the whole $50 per share above the strike is long-term gain. $50,000 at 15% = $7,500, and that is the only tax you ever pay.

Same shares, same prices: $14,895 as an NSO against $7,500 as an ISO. That gap is why the holding periods are worth planning around, and why exercising early, when the spread is small, is the standard advice.

The trap nobody warns you about: you owe the AMT in the year you exercise, in cash, on a paper gain. If the stock then falls, the tax bill does not. People were bankrupted by exactly this in 2000 and again in 2022.