Exercising Incentive Stock Options (ISOs) creates a "bargain element" that triggers Alternative Minimum Tax. This calculator estimates the net AMT owed on top of your regular tax.
Estimated AMT owed (above regular tax)
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Exercise cost (cash needed)
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Bargain element
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AMT exemption (after phase-out)
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AMTable income
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AMT (parallel tax)
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Regular tax (federal)
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The phantom income regular tax ignores
When you exercise an incentive stock option and hold the shares, regular federal income tax sees nothing happen. You paid the strike price, you got stock, no taxable event. The Alternative Minimum Tax sees something else entirely. The gap between the fair market value at exercise and the strike price you paid, called the bargain element, counts as income for AMT purposes even though no cash changed hands and you sold nothing. This is why people describe ISO exercise as phantom income. You can owe a real tax bill on a paper gain, and if the stock later falls, that bill does not go away on its own. This calculator estimates the AMT you would owe on top of your regular tax so the exercise does not blindside you in April.
How the parallel tax is built
AMT runs as a separate calculation alongside your regular tax, and you pay whichever is higher. It starts from your income plus the ISO bargain element, then subtracts a generous exemption. For 2026 the exemption is $88,100 for single filers and $137,000 for married couples filing jointly, but it phases out at 25 cents per dollar of AMT income once you cross $626,350 single or $1,252,700 joint. Whatever remains is taxed at 26% up to $232,600 and 28% above that. If the resulting AMT exceeds your regular federal tax, the difference is what you owe extra, and as covered below, that extra is not lost forever; it becomes a credit.
Exercising 5,000 options at a $23 spread
Take a single filer with $200,000 of taxable income who exercises 5,000 ISOs. The strike price is $2 and the shares are worth $25 at exercise, a spread of $23 a share. They hold the stock, so regular tax ignores the exercise, but AMT does not.
| Step | Amount |
|---|---|
| Cash to exercise (5,000 times $2 strike) | $10,000 |
| Bargain element (5,000 times $23 spread) | $115,000 |
| AMT income ($200,000 plus $115,000) | $315,000 |
| Less AMT exemption (full, below phase-out) | $88,100 |
| AMT base, taxed at 26% | $226,900 |
| Tentative AMT | $58,994 |
| Regular federal tax on $200,000 | $41,063 |
| Extra AMT owed (AMT minus regular tax) | $17,931 |
The exercise triggers about $17,931 of AMT on top of the regular tax bill, even though only $10,000 of cash left the bank and not a single share was sold. That is the trap in miniature: the tax on the paper gain is nearly double the cash cost of exercising. The chart contrasts the regular tax column with the taller AMT column; the shaded top of the AMT bar is the extra you write a check for.
Getting the AMT back later
The AMT you pay on an ISO exercise is not a pure loss. It generates a minimum tax credit, tracked on Form 8801, that you can apply in future years whenever your regular tax exceeds your AMT, often when you finally sell the shares. It is nonrefundable but carries forward indefinitely, so you reclaim it as your tax situation normalizes. The catch is cash flow: you may pay $17,931 this year and recover it slowly, a real cost of money even if you get every dollar back. The classic minimizing move is to exercise only enough shares each year to stay just under the point where AMT starts to bite.
How long must I hold ISO shares for the tax break?
To get the favorable long-term capital gains treatment that makes ISOs worthwhile, you must hold the shares at least two years from the grant date and at least one year from the exercise date. Meet both and your entire gain over the strike price is taxed at long-term capital gains rates when you sell, a qualifying disposition. Sell before either deadline and you have a disqualifying disposition: the bargain element becomes ordinary income on your W-2, you lose the preferential rate, but you also generally avoid the AMT problem because the income is recognized normally. Holding to qualify is what creates the AMT timing gap in the first place.
Where do I find the cash to exercise and pay the AMT?
This is the hardest practical problem with ISOs, especially at private companies where you cannot simply sell shares to raise cash. In the example, exercising costs $10,000 and the AMT adds nearly $18,000, so you need close to $28,000 of cash for stock you cannot yet sell. The mistake to avoid is exercising a huge grant in one year, getting hit with a five-figure AMT bill, and having no way to pay it. Model the exercise here before you act, and size it to cash you actually have.
What happens to my AMT if the stock crashes after I exercise?
This is the nightmare scenario that ruined many employees after the dot-com bust. If you exercise and hold, you owe AMT on the bargain element at exercise, and if the share price then collapses, the bill is still calculated on the high value at exercise, so you can owe tax on a gain that has evaporated. Selling the shares in the same calendar year you exercised turns it into a disqualifying disposition and eliminates the AMT preference, the usual escape hatch if the stock drops before year end. Once you cross into a new tax year you are largely stuck with the bill, though the resulting capital loss and the AMT credit provide partial relief over time.