ISO exercises and AMT, explained simply

2026 tax year · 6-minute read

Incentive stock options have a seductive tax feature: exercising them triggers no regular income tax. You pay tax later, when you sell — and if you hold long enough, at capital-gains rates. The catch is a parallel tax system called the Alternative Minimum Tax (AMT), and it has ruined more than a few exercise plans.

The bargain element

When you exercise ISOs, the difference between the stock's fair market value that day and your strike price is called the bargain element (or "spread"). Example: strike $15, FMV $85, 2,000 shares → $140,000 of bargain element.

For regular tax: nothing happens. For AMT: that $140,000 is added to your income as a "preference item." You now compute your tax two ways — regular and AMT — and pay whichever is higher.

How AMT is computed (the 60-second version)

1. Start with your regular taxable income, add back the bargain element (plus a few other items) → this is your AMT income.
2. Subtract the AMT exemption: $90,100 single / $140,200 married filing jointly in 2026.
3. Apply AMT rates: 26% on the first $244,500 above the exemption, 28% after that → this is your tentative minimum tax.
4. If tentative minimum tax exceeds your regular tax, you owe the difference as AMT.

Run your numbers through the ISO/AMT estimator — it walks this exact computation.

The 2026 phase-out change (important)

Starting in 2026, the AMT exemption begins shrinking at $500,000 of AMT income (single) or $1,000,000 (joint) — and it shrinks fast: 50 cents for every extra dollar, twice as aggressive as before. The exemption is fully gone at $680,200 single / $1,280,400 joint.

Practical meaning: a large ISO exercise that pushes your AMT income past $500k doesn't just add 26–28% tax on the spread — it also eats your exemption, raising your effective AMT rate further. Big exercises deserve a dry run before you click exercise.

The AMT credit: it's prepaid, not lost

AMT paid on ISO exercises generally generates a minimum tax credit (Form 8801) that you can use against regular tax in future years. Think of AMT as a timing difference, not a total loss — though "future years" is cold comfort when the bill is due April 15 with no cash from the exercise to pay it.

Three rules of thumb

1. Model before you exercise. The estimator takes 60 seconds; an AMT surprise takes a year to unwind.
2. Watch the calendar. Exercising early in the year gives you until December to decide whether to sell (a disqualifying disposition converts spread to ordinary income but can reduce AMT exposure — talk to a CPA).
3. Keep cash reserves. Never exercise an amount whose potential AMT bill you couldn't pay from savings. The stock can fall; the tax bill won't.