AMT and incentive stock options collide more often than most people expect, especially after a year of strong stock growth. The alternative minimum tax (AMT) is a separate tax calculation that runs alongside your regular tax return. Exercising incentive stock options (ISOs) is one of the most common ways to trigger it.
AMT and Incentive Stock Options: How the Two Connect
AMT exists as a parallel tax system with its own rules for what counts as income. Certain items excluded from regular taxable income still count for AMT purposes, and the ISO spread is one of them.
When you exercise ISOs, the spread between your strike price and the stock’s market value skips ordinary income tax entirely. But that same spread gets added back into your AMT income. You then calculate your tax both ways, under the regular system and under AMT, and pay whichever amount is higher. Eventually selling those shares for favorable long-term capital gains rates, called a qualifying disposition, requires holding them at least one year from exercise and two years from the original grant date. Both tests apply.
The ISO spread is invisible to your regular tax return but fully visible to AMT. A gain that costs you nothing under regular rules can still generate a real tax bill under AMT.
How AMT Actually Gets Calculated
AMT starts with your regular taxable income, adds back items like the ISO spread, then subtracts an AMT exemption amount that varies by filing status and phases out at higher income levels. What’s left is taxed at 26% up to a threshold and 28% above it.
If that AMT figure comes out higher than your regular tax liability, you owe the difference on top of your regular tax. If it doesn’t, AMT has no effect on your return that year.
The phase-out mechanics changed starting in 2026 under the One Big Beautiful Bill Act (OBBBA). For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married filing jointly. But the exemption now starts phasing out at $500,000 (single) or $1,000,000 (married), well below the 2025 thresholds of $626,350 and $1,252,700. The phase-out rate also doubled, from 25% to 50%. That means the exemption disappears twice as fast once you cross that line. The stated AMT rates stay at 26% and 28%, but losing the exemption this quickly pushes your effective marginal rate into the low-to-mid 30% range during the phase-out itself. If your income is anywhere near $500,000, a tax projection before exercising matters more in 2026 than it has in years.
Who This Applies To
This applies most directly to anyone exercising a meaningful batch of ISOs. It matters especially at a company where the stock price has risen well above the strike price. Higher earners feel it too, since a bigger regular tax bill sometimes still outpaces AMT and avoids the issue entirely.
It catches people off guard most often during a single large exercise late in the year. There’s little time left to plan around the resulting spread before December 31.
It’s also worth knowing that ISOs come with their own annual cap. Only $100,000 in fair market value, measured at the grant date, can become exercisable as ISOs in any calendar year. Anything above that limit becomes NSOs automatically, taxed as ordinary income at exercise instead of potentially qualifying for capital gains treatment. Employees with large grants at fast-growing companies run into this more often than they expect.
How This Plays Out
Sofia exercises 5,000 ISOs with a $3 strike price and the stock at $30. Her spread is $135,000, well above her exemption. For a high earner whose AMT exemption is already absorbed by other income, that spread can add close to $36,000 to her tax bill. That’s at a blended AMT rate of roughly 27%, even though it never shows up as ordinary income.
Sofia could have done this differently. Splitting the same 5,000 shares into two exercises across two calendar years, instead of one large exercise, would have kept each year’s AMT income lower. That can reduce or avoid the exemption phase-out and lower her total AMT bill compared to exercising everything at once.
If the stock price drops after you exercise but before December 31 of that same year, selling the shares can eliminate the AMT owed on that exercise. It also means the spread is taxed as ordinary income instead of receiving ISO treatment. That ordinary income is only the lesser of your original spread at exercise or your actual gain on the sale. If the stock has dropped below your exercise price by the time you sell, you recognize no ordinary income at all, only a capital loss. Waiting until January closes the AMT-elimination window and locks in the AMT bill even if the stock later falls further.
Action Steps Before You Exercise ISOs
- Calculate your expected spread before exercising, using your strike price and current market value.
- Run an AMT projection that includes your full income picture, not just the ISO spread.
- Consider splitting a large exercise across two calendar years to manage the AMT impact.
- Track the exercise date and year-end stock price in case a same-year sale becomes worth considering.
- Keep records of any AMT paid so you can claim the AMT credit in a future year if eligible.
- Work with a tax professional before a large exercise, since AMT calculations depend on your full return.
I’ve watched clients exercise a large ISO batch in December of a strong year, without realizing AMT was coming. The tax bill isn’t the problem. The lack of a plan is. A little modeling before you exercise gives you real choices, including timing, splitting the exercise, or exercising a smaller amount than your full vested balance.
Common Questions
What is the connection between AMT and incentive stock options?
Exercising ISOs adds the spread between your strike price and market value to your AMT income, even though that spread is excluded from regular taxable income. If your AMT ends up higher than your regular tax, you pay the AMT amount instead.
Do all ISO exercises trigger AMT?
No. A small spread relative to your income may stay under the AMT exemption threshold and trigger nothing. Larger spreads, especially at companies with significant stock appreciation, are far more likely to trigger AMT.
Can I get back the AMT I paid?
Often, yes, through the AMT credit, but only in a year when you’re not subject to AMT again. If you trigger AMT the following year too, the credit waits. The good news is it carries forward indefinitely until you can use it. Recovering it can take several years depending on your income, and it requires tracking on your tax return.
Can I undo an ISO exercise to avoid AMT?
Selling the shares before December 31 of the exercise year turns it into a disqualifying disposition, which can eliminate the AMT owed on that exercise, though it also gives up ISO tax treatment on the shares.
Does an 83(b) election apply to ISOs?
An 83(b) election matters most for early-exercised options before vesting, ISO or NSO. I cover when it’s worth filing in a separate post on the 83(b) election.
How do I know if I’ll owe AMT before I exercise?
Running an AMT projection with your expected spread and total income before you exercise is the most reliable way to know. A tax professional can model this using your specific numbers.
Where to Go From Here
AMT is easier to plan around once you understand the basics of how to exercise stock options and stock option exercise tax more broadly. For the full picture, visit my Equity Compensation pillar page, and revisit RSU vs. Stock Options, ISO vs. NSO, and How Stock Option Vesting Actually Works. For the IRS’s own explanation of how AMT is calculated, see Topic No. 556. To learn more about how I work with clients, visit my services page.
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