The AMT exists to make sure high earners with large deductions or certain types of income can’t reduce their tax bill to almost nothing using the regular tax rules. For stock option holders, the part that matters most is that exercising incentive stock options (ISOs) can trigger it, sometimes creating a real, immediate tax bill on paper gains you can’t yet access. This post covers how AMT works, what triggers it, and how to estimate what you might owe.
What is the AMT?
The AMT is a separate tax calculation that runs alongside your regular income tax. You calculate your tax both ways, under the regular rules and under the AMT rules, and pay whichever amount is higher. It exists specifically to add back certain deductions and income items that the regular tax system treats favorably, and the spread from exercising ISOs is one of those items.
How does exercising ISOs trigger AMT?
When you exercise an ISO, the difference between your strike price and the stock’s current fair market value, called the spread, doesn’t count as regular taxable income. But it does count as an “AMT preference item,” meaning it gets added into a separate AMT income calculation even though no cash changed hands and you haven’t sold anything. If that AMT calculation ends up higher than your regular tax bill for the year, you owe the difference.
What is the AMT exemption, and how much can I earn before owing it?
The AMT system includes an exemption amount that shields your first chunk of AMT income from tax entirely. For 2026, that exemption is $90,100 for single filers and $140,200 for married couples filing jointly. Above certain income levels ($500,000 single, $1,000,000 joint for 2026), the exemption itself starts phasing out, meaning higher earners get less protection from it.
How is AMT actually calculated?
Once your AMT income exceeds your exemption amount, the excess is generally taxed at 26%, rising to 28% on larger amounts. In practice, this means a big ISO exercise can create real, immediate tax liability that has nothing to do with whether the shares are worth anything you can actually spend, since private company stock typically can’t be sold on the spot.
What is the AMT credit, and do I get that money back?
Yes, in a sense. AMT paid because of an ISO exercise generally becomes a credit you can use in future years to offset your regular tax bill, once your regular tax exceeds what your AMT would be. This is meant to prevent true double taxation over time, but the credit only helps once you have enough regular tax liability to use it against, which can take years, especially if the company never has a liquidity event and the stock never becomes sellable.
Does exercising NSOs trigger AMT?
No. NSOs don’t create an AMT preference item at exercise. Instead, the spread is taxed immediately as ordinary income, which is a different mechanism with its own upfront cost. Neither path avoids paying tax on the spread eventually, they just differ in when and how.
Worked example
Say you exercise 15,000 ISOs with a $4 strike price when the fair market value is $16 a share. The spread is 15,000 times ($16 minus $4), or $180,000, which becomes AMT income for the year.
For a single filer with no other AMT income, subtracting the $90,100 exemption leaves $89,900 subject to AMT at 26%, or roughly $23,374 owed, using 2026 figures. That’s real cash due by tax time, even though the shares themselves can’t be sold to cover it if the company is still private. This is a simplified estimate. Your actual AMT depends on your total income, filing status, and other preference items, so it’s worth running your specific numbers with a tax professional before exercising a large batch of ISOs.
FAQ
Do I owe AMT just for holding ISOs? No. AMT is only triggered when you exercise ISOs, not simply by having them granted or vested.
Can I avoid AMT entirely? Exercising NSOs instead of ISOs avoids AMT specifically, but creates ordinary income tax instead, which is often a similar or larger cost. Exercising smaller batches of ISOs over multiple years, staying under the exemption amount each year, is another approach some people use, though it depends on your specific situation.
Do I get the AMT money back if the company fails? Not directly. The AMT credit only offsets future regular tax liability, so if you never have enough future income to use it against, or the company fails and the stock becomes worthless, the AMT you paid isn’t refunded, though you may be able to claim a capital loss in some circumstances.
Is AMT the same as capital gains tax? No. AMT is a separate calculation triggered at exercise for ISOs. Capital gains tax applies later, when you actually sell the shares.
How do I know if I’ll owe AMT before I exercise? It depends on your total income, filing status, and the size of the spread on the options you’re exercising. Tax software or a tax professional can model this before you commit to exercising.
What to do next
The exact AMT impact of exercising depends on your full financial picture, not just the spread on one grant. You can model your own exercise costs and estimated AMT at movewealth.io.
MoveWealth is not a broker-dealer, investment adviser, or lender. This is educational content, not financial, tax, or legal advice. Consult a qualified professional about your specific situation.