How stock options are taxed when you exercise depends on which kind you hold. Non-qualified stock options (NSOs) are taxed as ordinary income the moment you exercise, on the spread between the exercise price and the stock’s fair market value that day. Incentive stock options (ISOs) owe no regular income tax at exercise, but the same spread is picked up by the alternative minimum tax and can produce a real bill in April. Everything else about option taxation flows from that split.
What You Owe When You Exercise an NSO
Exercise an NSO and the spread is treated exactly like additional wages. If your exercise price is $10 and the stock is worth $40, the $30 per share is ordinary income in the year you exercise. Your employer withholds federal income tax, Social Security, and Medicare on it and reports the amount in Box 1 of your W-2.1Internal Revenue Service. Instructions for Form 6251
Federal withholding on the spread is usually done at the supplemental wage rate of 22%, or 37% on supplemental wages above $1 million for the year. If exercising pushes you into a higher marginal bracket, that flat rate will undershoot, and you’ll owe the difference at filing. Plan for the shortfall before you exercise, not after.
The ordinary income you recognize becomes part of your cost basis in the shares. In the example above, your basis is $40: the $10 you paid plus the $30 already taxed as wages. That number matters when you sell, because brokers routinely get it wrong.
What You Owe When You Exercise an ISO
Exercise an ISO and, for regular federal income tax purposes, you owe nothing. There is no withholding, and nothing lands on your W-2. If you hold the shares long enough after exercise, the entire profit can eventually be taxed at long-term capital gains rates rather than ordinary income rates. That is the whole reason ISOs exist.
The AMT Adjustment
The spread at exercise is still visible to a second tax system. The alternative minimum tax adds the bargain element back into your income for AMT purposes, even though the regular tax system ignores it.2Office of the Law Revision Counsel. 26 USC 56 – Adjustments in Computing Alternative Minimum Taxable Income You run the AMT calculation on Form 6251, and if your tentative minimum tax exceeds your regular tax, you pay the difference.1Internal Revenue Service. Instructions for Form 6251
For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, phasing out at $500,000 and $1,000,000 respectively.3Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 The AMT rate is 26% on the first $244,500 of AMT income above the exemption and 28% above that. A large ISO exercise can push you well past the exemption and produce a five- or six-figure tax bill with zero cash proceeds to pay it. That mismatch, tax due on paper gains you never sold, is where most ISO planning fails.
Two Bases and a Credit That Comes Back Later
Exercising ISOs gives the same shares two cost bases. Your regular tax basis is the exercise price you paid. Your AMT basis is the fair market value on the exercise date, since you already picked up the spread for AMT purposes. When you eventually sell, the AMT gain is smaller than the regular tax gain, which is how the system begins refunding what you fronted.
AMT paid because of an ISO exercise also generates a minimum tax credit that carries forward. You claim it on Form 8801 in any later year your regular tax exceeds your tentative minimum tax.4Internal Revenue Service. About Form 8801, Credit for Prior Year Minimum Tax – Individuals, Estates, and Trusts The credit only offsets AMT caused by timing differences like ISO exercises, not permanent preference items.5Internal Revenue Service. Instructions for Form 8801 Recovering the full credit often takes several years, depending on how your income moves.
How the Later Sale Is Taxed
Exercising is only the first tax event. Selling the shares is the second, and the treatment there depends on the option type and how long you held.
For NSO shares, the gain or loss on sale is the difference between the sale price and your adjusted basis (exercise price plus the ordinary income already taxed). The holding period starts the day after exercise. Sell within a year and it’s a short-term capital gain at ordinary rates. Hold more than a year and long-term rates of 0%, 15%, or 20% apply, depending on taxable income.6Internal Revenue Service. Topic No. 409, Capital Gains and Losses The 20% rate kicks in above $545,500 of taxable income for single filers and $613,700 for joint filers in 2026.3Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
For ISO shares, the payoff shows up only if you satisfy two holding periods: more than two years from the grant date and more than one year from the exercise date.7Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options Meet both and the entire gain from exercise price to sale price is a long-term capital gain. Miss either and you have a disqualifying disposition: the spread at exercise becomes ordinary income, and only any additional appreciation is capital gain. If the stock fell and you sell below the exercise-date value, the ordinary income is capped at your actual gain, so you aren’t taxed on a spread you never realized.
Cashless Exercise and Early Exercise
Same-Day Sale
A cashless exercise means exercising and immediately selling enough shares to cover the strike price and taxes, often in one broker transaction. For NSOs, the tax result is the same as any other exercise: the spread is ordinary income, and because you sold at the same price used to compute the spread, there’s no capital gain or loss on top. You just don’t need cash upfront.
For ISOs, a same-day sale is always a disqualifying disposition. You cannot satisfy the one-year post-exercise holding period if you sell the day you exercise. The spread becomes ordinary income and the ISO benefit is gone. If a cashless exercise is your plan, holding ISOs rather than NSOs didn’t buy you anything.
Early Exercise With an 83(b) Election
Some companies let you exercise before vesting. Without any election, tax is measured at each vesting date rather than at exercise. A Section 83(b) election lets you accelerate the tax event to the exercise date, so you include the spread in income for the year you receive the shares even though they’re unvested.8Office of the Law Revision Counsel. 26 USC 83 – Property Transferred in Connection With Performance of Services The point of doing this is to exercise when the spread is tiny or zero, pay little or no tax then, and start the long-term capital gains clock immediately.
The deadline is 30 days from the transfer date. No extensions, no exceptions. You file the election with the IRS using Form 15620 and give a copy to your employer. Miss the window and the election is void. The other risk: if you leave before vesting and forfeit the shares, you don’t get back the tax you already paid. An 83(b) election is a bet on the stock and on your own tenure.
The 3.8% Net Investment Income Tax
Capital gains from selling option shares can also be hit with the net investment income tax when modified adjusted gross income exceeds $200,000 for single filers or $250,000 for joint filers.9Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax The tax is 3.8% of the lesser of your net investment income or the amount your MAGI exceeds the threshold, and those thresholds are not indexed for inflation.10Internal Revenue Service. Questions and Answers on the Net Investment Income Tax
Gains from shares acquired through stock options count as net investment income.11Internal Revenue Service. Topic No. 559, Net Investment Income Tax That makes the top federal rate on long-term capital gains effectively 23.8%, not 20%. The ordinary income from an NSO exercise isn’t itself subject to the 3.8% tax, but it does raise your MAGI, which can drag your other investment income into the NIIT for that year.
Reporting the Exercise Correctly
For NSOs, the exercise flows through your W-2 automatically. For ISOs, there’s no W-2 impact, but your employer files Form 3921 reporting the exercise price, the fair market value at exercise, and the number of shares.12Internal Revenue Service. About Form 3921, Exercise of an Incentive Stock Option Under Section 422(b) You use the Form 3921 figures to compute the AMT adjustment on Form 6251.1Internal Revenue Service. Instructions for Form 6251
When you sell, the broker issues Form 1099-B with the proceeds and a cost basis.13Internal Revenue Service. Instructions for Form 1099-B The basis is frequently wrong for option shares. For NSOs, brokers often report only the exercise price, leaving out the ordinary income already taxed through your W-2. Fail to correct this on Form 8949 and you pay capital gains tax a second time on income the IRS already taxed as wages. For a disqualifying ISO disposition, brokers typically report just the exercise price and ignore the ordinary income piece. For a qualifying ISO disposition, the reported basis is the exercise price, but you still need to reconcile the separate AMT basis when calculating any minimum tax credit.
You report the corrected numbers on Form 8949, which feeds Schedule D. Pull the ordinary income figure from your W-2 for NSOs, or from Form 3921 for ISOs, to build the correct adjusted basis. If you paid AMT on a prior ISO exercise, file Form 8801 in any year your regular tax exceeds your tentative minimum tax to recover the credit.4Internal Revenue Service. About Form 8801, Credit for Prior Year Minimum Tax – Individuals, Estates, and Trusts Skipping the basis adjustment on Form 8949 is the most common and most expensive reporting mistake with stock options. The IRS will keep the overpayment; it will not flag it for you.