ISOs and AMT: why exercising can trigger a tax bill (and what to consider)

What an ISO actually is

An incentive stock option, or ISO, is a right your employer grants you to buy company stock at a fixed price (the strike price or exercise price), usually the fair market value on the day you were granted the option. ISOs are a specific type of option defined in the tax code, and only employees can receive them. They are different from non-qualified stock options (NSOs), which follow different and generally simpler tax rules.

Three moments matter in an option's life:

• Grant is when the company gives you the option. Generally, nothing is taxed at grant.
• Exercise is when you actually buy the shares at your strike price. This is the moment that matters for AMT.
• Sale is when you sell the shares you bought. How long you held them decides whether the gain is taxed at favorable long-term rates.

The appeal of an ISO is that, if everything lines up, you can turn the growth in your shares into long-term capital gain rather than ordinary income. The catch lives in the middle moment, exercise, where AMT can show up.

The bargain element: the number that drives everything

When you exercise, the shares are usually worth more than your strike price. That gap is the bargain element:

For regular income tax, this number does nothing when you exercise an ISO and hold the shares. You report no income and pay no regular tax that year. That is the whole point of an ISO's favorable treatment.

For AMT, though, the bargain element is treated as income in the year you exercise. The tax code essentially says: for this parallel calculation, pretend you received that spread. That single difference is why ISOs and AMT are talked about in the same breath.

What the alternative minimum tax is

AMT is a second, parallel way of calculating your federal income tax. It was designed to keep people with certain large deductions or preference items from paying too little. Each year, in simplified terms, you figure your tax two ways:

• The regular way, with your ordinary brackets and deductions.
• The AMT way, which starts from a broader income base (adding back items like the ISO bargain element), subtracts an AMT exemption amount, and applies the AMT rates.

You pay whichever is higher. In a year with a large ISO bargain element, the AMT calculation can come out higher, and the difference is what people call "getting hit with AMT."

The AMT system uses an exemption amount that phases out at higher income levels, and it applies its own two-tier rate schedule. For 2026, the exemption is $90,100 for single filers and $140,200 for married couples filing jointly. The AMT rate is 26% up to roughly $244,500 of the AMT base and 28% above that. These figures are adjusted for inflation, so the exact numbers depend on the year and your filing status.

The catch is the phase-out. Once your income climbs past a threshold, that exemption starts disappearing, which is how high earners with a large ISO exercise get pulled into AMT. For 2026, the exemption begins phasing out at $500,000 (single) and $1,000,000 (married filing jointly).

A simple example

These numbers are round and purely illustrative, not a prediction of your result. Say you have an ISO to buy 10,000 shares at a strike price of $2, and the shares are worth $20 when you exercise.

You paid $20,000 to exercise and received no cash. For regular tax, you generally report nothing in the year of exercise. For AMT, you have $180,000 of additional income to run through the parallel calculation. Depending on the rest of your return, that can produce a sizable AMT bill due the following April, even though you never sold a share. This is the surprise that catches people, and it is exactly the kind of thing worth modeling before you exercise rather than after.

What happens when you sell: qualifying vs disqualifying

How you are taxed when you eventually sell depends on how long you held the shares. The ISO rules set two holding periods that both have to be met for the most favorable treatment:

• At least two years from the grant date, and
• at least one year from the exercise date.

Meet both and you have a qualifying disposition: your gain over the strike price is generally taxed as long-term capital gain. Miss either one and you have a disqualifying disposition: some or all of the spread is pulled back into ordinary income. When that sale happens in the same year as the exercise, it generally sidesteps the AMT adjustment on those shares, because the income shows up in the regular system instead. (Sell in a later year and the AMT adjustment from the exercise year can still apply.)

That trade-off, favorable long-term rates with possible AMT on one side and ordinary rates with the AMT adjustment often avoided on the other, is the heart of ISO planning. There is no single right answer; it depends on your numbers, your other income, and how much risk you want to carry in a single stock. The point of planning is to see the trade-off clearly before you act.

The AMT credit: you may get some of it back

AMT triggered by exercising and holding ISOs is often not a permanent extra tax. Because it comes from a timing difference (the bargain element is income for AMT now, but not for regular tax until you sell), paying it can generate a minimum tax credit. In later years, when your regular tax is higher than your AMT, that credit can offset regular tax, sometimes recovering the AMT over time.

There is an important related wrinkle: your cost basis in the shares can be different for regular tax and for AMT. The AMT basis includes the bargain element you already counted, which matters when you sell and helps avoid being taxed on the same gain twice. Tracking both bases carefully is one of the least glamorous and most valuable parts of getting ISOs right.

How quickly, and whether, the credit comes back depends entirely on your future returns, so it is best thought of as "possible recovery over time," never a guarantee.

ISO and AMT questions people ask

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