Incentive stock options have the best tax treatment of any common form of equity pay. Exercise them and you owe no regular income tax at all. Hold the shares long enough and the entire gain is taxed at long-term capital gains rates. The catch has a name, the alternative minimum tax, and it has caught out a lot of people over the years.
The AMT doesn't make ISOs a bad deal. It makes them a planning problem. How many options you exercise, and in which year, decides whether you pay nothing extra, a manageable amount, or a large bill on paper gains that may later disappear.
This article explains how ISOs are taxed, then works through the 2026 AMT numbers for a typical household so you can see where the line sits.
Three moments, three different tax results
Grant. Nothing happens. You've been given the right to buy shares at a fixed price, the strike price, usually the stock's value on the grant date.
Exercise. You pay the strike price and receive shares. The difference between the share price that day and the strike price is called the spread. For non-qualified options, the spread is taxed as wages right away. For ISOs it isn't: no regular income tax, no Social Security, no Medicare, and nothing withheld. But the spread is counted as income for the AMT.
Sale. If you hold the shares for more than two years from the grant date and more than one year from the exercise date, the sale is a qualifying disposition. Your whole gain above the strike price is long-term capital gain. Sell earlier and it's a disqualifying disposition, which turns part of the gain into ordinary income. More on that below.
How the AMT works, briefly
The AMT is a second tax calculation that runs alongside the normal one. It starts from your regular income, adds back certain items (the ISO spread is the big one for most people), subtracts a flat exemption instead of the standard deduction, and applies rates of 26% and 28%. The result is your "tentative minimum tax." If that's higher than your regular tax, you pay the difference as AMT.
For 2026, the exemption is $140,200 for married couples filing jointly and $90,100 for single filers. It starts phasing out at $1,000,000 and $500,000 of AMT income respectively, so for most households with ISOs the full exemption applies.
Most people never pay AMT because their regular tax is comfortably above their tentative minimum tax. An ISO exercise narrows that gap, and past a certain point it closes it.
Finding the crossover
Take a married couple with $250,000 of wages, no other income and the standard deduction. Their 2026 regular taxable income is $217,800 and their regular federal tax is $37,468.
On the AMT side, their income is $250,000, since the standard deduction doesn't apply, less the $140,200 exemption, leaving $109,800. At 26%, their tentative minimum tax is $28,548. That's about $8,900 below their regular tax, so no AMT.
Every dollar of ISO spread they create raises the AMT figure by 26 cents and the regular figure by nothing. The two meet when the spread reaches about $34,300. That's the amount of spread this couple can exercise in 2026 without paying any AMT at all. Below that line, exercising is free for them. Above it, each extra dollar of spread costs 26 cents of AMT in the year of exercise.
Now suppose they exercise 2,000 options with a $10 strike price when the stock is at $60. The spread is $100,000. Their AMT income becomes $350,000, the taxable amount after the exemption is $209,800, and the tentative minimum tax is $54,548. Subtract the $37,468 regular tax and they owe $17,080 of AMT.
On top of that, they need $20,000 in cash to pay the strike price. That's $37,080 out of pocket for shares they haven't sold, in a stock that can move a long way before the holding periods are up.
Your own crossover depends on your income, deductions and filing status. People who itemize often hit it sooner, because state and local taxes aren't deductible under the AMT. The method is the same, though: work out the gap between your regular tax and your tentative minimum tax, divide by 0.26, and that's roughly how much spread you can exercise for free.
The AMT credit: some of it comes back
AMT caused by ISOs isn't always lost money. Because the ISO spread is a timing difference rather than a permanent one, the AMT it creates becomes a minimum tax credit you carry forward. In later years, when your regular tax is higher than your tentative minimum tax, you can use the credit to cut your regular tax. Form 8801 tracks it.
The year you sell the shares is often when a lot of it comes back. For the AMT, your basis in the shares is their value at exercise, $60 in the example. For regular tax, it's the $10 strike. Sell at $80 in a qualifying disposition and you report a $140,000 gain for regular tax but only a $40,000 gain for the AMT. That difference usually pushes your regular tax well above your tentative minimum tax for the year, which is exactly the room the credit needs.
So the realistic picture is that ISO AMT works like a loan to the IRS. You pay it up front, and you get it back later as long as the shares hold their value and your income cooperates.
The scenario that goes wrong
The loan only comes back cleanly if the shares are still worth something when you sell. The well-known disasters from the 2000 tech crash all followed the same pattern: exercise a large block, hold for long-term treatment, pay AMT on a big paper gain, then watch the stock collapse.
Run it with the example. The couple pays $17,080 of AMT on shares valued at $60. A year later the stock is at $15. Their real gain is $10,000, but they've already paid AMT on $100,000 of spread. The credit is still there, but with a modest income it may come back only slowly, and the capital loss for AMT purposes is subject to the same $3,000-a-year limit against other income as everything else. People have spent a decade recovering AMT paid on gains that vanished in months.
The December escape hatch
There's a useful way out if the price falls in the same calendar year you exercised. Sell the shares before December 31. That's a disqualifying disposition, and when it happens in the exercise year, the AMT adjustment disappears completely. Better still, when you sell at a price below the exercise-day value, the ordinary income is limited to your actual gain over the strike price, not the full original spread.
This is one reason many planners like exercising early in the year. If the stock falls by autumn, you can still unwind the position with a same-year sale. Exercise in December and that option is gone.
Disqualifying dispositions in later years
If you sell after the exercise year but before both holding periods are met, the sale is disqualifying. The spread at exercise becomes ordinary income in the year of the sale, and anything above the exercise-day value is capital gain. If the sale price is lower than the exercise-day value, the ordinary income is limited to the actual gain.
A couple of things make disqualifying income from ISOs different from wages. No Social Security or Medicare tax applies, and employers aren't required to withhold income tax on it. It still shows up on your W-2, but you'll usually need an estimated payment to cover it.
The AMT you paid in the exercise year doesn't vanish here either. It becomes a credit, and the disqualifying sale typically creates the room to use it.
The rules that change what you have
The $100,000 limit. Only $100,000 worth of ISOs, measured at the grant-date value, can first become exercisable in any one calendar year. Anything above that is automatically treated as non-qualified options, taxed as wages at exercise. Large grants often contain both kinds, and your stock plan statement should show which is which.
Leaving the company. ISOs have to be exercised within three months of leaving your job to keep ISO status, or within a year if you leave because of disability. Some plans let you exercise for longer, but anything exercised after the three-month window is taxed as a non-qualified option.
Early exercise and 83(b). Some private companies let you exercise options before they vest. If you do, filing an 83(b) election within 30 days locks in the AMT spread at exercise, which is often zero for early-stage grants. Miss the deadline and the spread is measured as each tranche vests, possibly at much higher prices. The 30 days are strict.
The paperwork. Your employer sends Form 3921 for every year you exercise ISOs. It shows the grant date, exercise date, strike price and share value at exercise, which is everything you need for both the AMT and the eventual sale. Keep them.
State tax. A few states have their own version of the AMT, and they don't all treat ISOs the same way. Check your state's rules before assuming the federal crossover is the only number that matters.
What to actually do
Each year, before you exercise, estimate your crossover. Exercising up to it costs nothing and starts the holding-period clocks on those shares. Doing that every year, rather than letting options pile up for one large exercise, is the simplest way to keep AMT small.
If you want to exercise beyond the crossover, size it to the cash you can afford to lose. Count the strike price and the AMT together, and assume the AMT might take years to come back.
Exercise early in the calendar year when you can, so a same-year sale remains available if the price drops. And treat the holding decision the way you'd treat any other: the tax benefit of a qualifying sale is real, but it doesn't change the risk of holding a large position in one company. If that position has grown big, our article on reducing a concentrated stock position picks up from here.