How stock options are taxed depends first on which type your employer gave you. Non-qualified stock options (NSOs) create ordinary income the moment you exercise, taxed at your regular income tax rate and subject to payroll withholding. Incentive stock options (ISOs) let you exercise without owing regular federal income tax and can convert the entire gain to long-term capital gains rates if you hold the shares long enough, but they carry an Alternative Minimum Tax trap that catches many people off guard. Your grant paperwork will say which type you hold, and that single fact drives almost every tax decision that follows.
Non-Qualified Stock Options: Tax at Exercise
NSOs are taxed under Section 83 of the Internal Revenue Code, which treats the value you get from exercising as compensation for services.1Office of the Law Revision Counsel. 26 USC 83 – Property Transferred in Connection With Performance of Services Nothing is owed at grant. Tax hits when you exercise, and it hits on the spread: the difference between the stock’s market price on the exercise date and the strike price you paid.
That spread is ordinary income in the year of exercise. Your employer withholds federal income tax, Social Security tax at 6.2%, and Medicare tax at 1.45%.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates If your total wages for the year exceed $200,000, an extra 0.9% Medicare surtax applies to the excess. State withholding usually applies too.
After exercise, your cost basis in the shares equals the fair market value on the exercise date, not the strike price. The spread you already paid ordinary income tax on is baked into your basis. Any further gain or loss when you eventually sell is a capital gain or loss, short-term or long-term depending on how long you hold after exercise.
Cashless Exercise
Most employees don’t have the cash to pay the strike price plus withholding. A cashless exercise (sometimes called a same-day sale) has the broker sell enough shares immediately to cover the strike price, taxes, and commissions, then delivers what’s left. A sell-to-cover variation sells only enough to pay the costs and keeps the rest of the shares in your account. Either way, the full spread is taxable in the year of exercise regardless of how many shares you keep.
Incentive Stock Options: No Regular Tax at Exercise
ISOs are governed by Section 422 and follow a different track.3Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options Exercising an ISO does not trigger regular federal income tax. No income tax withholding, no Social Security, no Medicare tax on the spread. You buy the shares at the strike price and, for regular tax purposes, owe nothing.
The tax event is the sale. If you meet both holding periods, the entire gain from your strike price to your sale price qualifies for long-term capital gains rates of 0%, 15%, or 20% depending on your taxable income.4Internal Revenue Service. Topic No. 409, Capital Gains and Losses Ordinary income rates climb to 37%, so the difference in treatment can be large on a big exercise.
The catch is the Alternative Minimum Tax.
The AMT Trap
The ISO spread that avoids regular income tax counts as an adjustment for the Alternative Minimum Tax.5Office of the Law Revision Counsel. 26 USC 56 – Adjustments in Computing Alternative Minimum Taxable Income AMT runs in parallel with the regular tax system, and you pay whichever is higher. Its rates are 26% and 28%, and its exemption phases out at higher income levels, so a large ISO exercise can put you into AMT even if your salary alone wouldn’t.
The spread is reported on line 2i of Form 6251.6Internal Revenue Service. Instructions for Form 6251 The painful version of this scenario: you exercise, receive no cash, owe no regular income tax, and then discover you owe thousands in AMT on shares you haven’t sold. Running the AMT calculation before you exercise is the single most effective way to avoid a surprise bill.
Recovering AMT You Paid
AMT paid because of an ISO exercise generates a minimum tax credit you can carry forward. You claim it on Form 8801 in any later year where your regular tax exceeds your AMT liability.7Internal Revenue Service. Instructions for Form 8801 The credit doesn’t expire. Often you recover it in the year you sell the ISO shares, because the sale raises your regular tax above the AMT figure. File Form 8801 every year you have an unused balance; the IRS won’t apply it for you.
Holding Periods and Disqualifying Dispositions
The capital gains treatment on ISOs depends on two holding periods. You must hold the shares for at least two years after grant and more than one year after exercise.3Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options Both must be met. A sale that satisfies both is a qualifying disposition, and the full gain is long-term capital gain.
Selling before either deadline is a disqualifying disposition. The spread at exercise is reclassified as ordinary income and reported on your W-2 for the year of sale. It is not subject to Social Security or Medicare tax, which distinguishes it from an NSO exercise. If the stock dropped between exercise and sale, the ordinary income is limited to your actual gain on the sale rather than the full exercise-date spread. Any gain above the exercise-date fair market value is capital gain; a loss below it may be deductible.
The $100,000 ISO Limit
Federal law caps the amount of stock that can receive ISO treatment in any calendar year. If the total fair market value at grant of shares that first become exercisable in a single year exceeds $100,000, the excess is automatically treated as NSOs.3Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options Reclassification runs in grant order, earliest first. If you hold multiple ISO grants, tracking the grant-date value of each tranche as it vests is the only way to know which shares still qualify.
The Net Investment Income Tax
A separate 3.8% surtax can apply on top of everything else. The Net Investment Income Tax hits individuals whose modified adjusted gross income exceeds $200,000 (single), $250,000 (married filing jointly), or $125,000 (married filing separately).8Internal Revenue Service. Topic No. 559, Net Investment Income Tax The 3.8% applies to the lesser of your net investment income or the amount your modified AGI exceeds the threshold. Capital gains from stock sales are net investment income, so for high earners the NIIT effectively raises the top long-term capital gains rate from 20% to 23.8%. These thresholds are not indexed for inflation.9Internal Revenue Service. Questions and Answers on the Net Investment Income Tax
The Section 83(b) Election for Early Exercise
Some startups let you exercise options before they vest. Exercising early on unvested shares would normally defer tax under Section 83 until each tranche vests, potentially at a much higher stock price.1Office of the Law Revision Counsel. 26 USC 83 – Property Transferred in Connection With Performance of Services
A Section 83(b) election overrides that default. You choose to recognize the spread as income at the time of transfer, when the tax bill is usually smallest. If the stock climbs during vesting, you avoid recognizing that appreciation as ordinary income. For ISOs, filing 83(b) at early exercise when strike equals fair market value means zero taxable income at the time, and the holding period clocks for a qualifying disposition start running immediately.
The deadline is absolute. You must file within 30 days of the transfer date.10Internal Revenue Service. Form 15620, Section 83(b) Election No extension, no late-filing option. Weekend or holiday deadlines roll to the next business day, and that’s the only flexibility. The election is irrevocable.
The risk is real. If you file, pay tax, and then forfeit the shares because you leave before vesting, you cannot get the tax back. The law provides no refund. The election pays off when the stock appreciates and is a pure loss if you leave early or the company fails.
What Happens When You Leave the Job
Most option agreements give a limited window to exercise after employment ends. Ninety days is standard. For ISOs, exercising within 90 days of termination is a legal requirement to keep ISO tax treatment.3Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options Wait longer, and any ISOs you exercise convert to NSOs automatically. The spread becomes ordinary income with payroll withholding.
Some employers extend the post-termination window as a benefit. That extension is generous but creates a trap: extending the exercise period is treated as a modification, effectively a new grant. If the stock price has risen above the original strike, the modified option no longer qualifies as an ISO because ISOs must be granted at or above fair market value. It converts to an NSO by operation of law, no matter how long you later hold the shares.
For permanent and total disability, the exercise window extends to one year. If the option holder dies, the options can generally be exercised by the estate or heirs until the option’s original expiration date, and the ISO holding period requirements are waived entirely for the deceased employee’s shares.11Office of the Law Revision Counsel. 26 USC 421 – General Rules
Reporting the Sale Without Paying Tax Twice
The most expensive mistake in stock option taxation happens on Form 8949. When you sell shares acquired through options, the sale goes on Form 8949 and flows into Schedule D.12Internal Revenue Service. About Schedule D (Form 1040), Capital Gains and Losses Your broker’s Form 1099-B will typically show a cost basis equal to the strike price you paid, not the fair market value at exercise. For NSOs, that ignores the ordinary income you already reported and paid tax on. If you enter the broker’s basis without adjusting it, you pay tax twice on the same income.
The fix: enter the broker’s reported basis in column (e) of Form 8949, use adjustment code “B” in column (f), and enter the correction in column (g).13Internal Revenue Service. Instructions for Form 8949 The adjustment equals the ordinary income you already recognized at exercise. For options granted after 2013, the IRS expects you to make this adjustment because the broker’s reported basis will not include the income component.
The other forms to know: your employer files Form 3921 for each ISO exercise and gives you a copy showing the grant date, exercise date, exercise price, and fair market value at exercise.14Internal Revenue Service. Instructions for Forms 3921 and 3922 Ordinary income from NSO exercises or ISO disqualifying dispositions shows up on your W-2. If you exercised ISOs during the year, complete Form 6251 to see whether you owe AMT, and file Form 8801 in any year you have an unused minimum tax credit carryforward.