Step 1: exercising and holding owes no regular tax
When you exercise an ISO and keep the shares, you pay nothing in regular income tax on the spread between the market value and your strike price. That's the ISO advantage, and it's real. The problem is a second, parallel tax system.
Step 2: the paper gain is an AMT preference
The bargain element — market value at exercise minus what you paid — is added to your income under the Alternative Minimum Tax (Form 6251). You didn't sell anything and got no cash, but the AMT counts the paper gain anyway. Exercise 10,000 options with a $20 spread and you've just added $200,000 of AMT income out of nowhere.
Step 3: the 2026 AMT math
Your AMT income gets an exemption — $90,100 (single) or $140,200 (married filing jointly) for 2026. But after the 2025 OBBB law, that exemption phases out at 50 cents per dollar of AMT income above $500,000 (single) or $1,000,000 (joint) — twice the old phaseout speed, so high earners lose it fast. AMT is then 26% of the base up to $244,500 and 28% above. You owe AMT only to the extent this tentative minimum tax exceeds your regular tax — which is exactly what a big ISO exercise causes.
How to avoid or soften the trap
Several levers, and a calculator makes them concrete: exercise fewer shares to stay just under your AMT "crossover" point; exercise early when the spread (and so the preference) is tiny; spread exercises across multiple tax years; or do a same-year (disqualifying) sale, which removes the AMT preference entirely and taxes the spread as ordinary income instead. The right move depends on your numbers — model them before you click exercise.
The silver lining: the Minimum Tax Credit
AMT you pay because of an ISO exercise isn't necessarily gone. It usually creates a Minimum Tax Credit (Form 8801) that reduces your regular tax in future years when your regular tax exceeds your tentative minimum tax. It's often a timing cost — you recover it over time — but you still need the cash the year you exercise.
One more wrinkle: dual basis
Because you were taxed differently under the two systems, your shares carry two cost bases: your strike price for regular tax, and the higher market-value-at-exercise for AMT. When you finally sell, your AMT gain is smaller than your regular gain, generating a negative AMT adjustment that year. It's how the system trues up — but it's why ISO sales need careful reporting.
See your AMT before you exercise → Free calculator: enter your options, strike, market value and income — see the exact AMT, and try different share counts to find your crossover.