How the 2026 AMT Rules Changed: Why More ISO Holders Will Owe It

If you exercise incentive stock options in 2026, the Alternative Minimum Tax math is not the same as it was in 2025. The One Big Beautiful Bill Act (OBBBA, enacted as H.R.1) kept the larger AMT exemption but reset how fast that exemption disappears at higher incomes. It now phases out sooner, and at twice the speed. The same ISO exercise that stayed clear of AMT last year can trigger it this year.

This article covers what moved, the exact 2026 figures, and the timing decisions that matter before December 31.

What changed for 2026

The AMT is a parallel tax calculation. You run your taxes the normal way, run them again under AMT rules, and pay whichever is higher. When you exercise ISOs and hold the shares, the bargain element (the gap between the fair market value and your strike price) is invisible to regular tax but counts as income under AMT. That single line is why ISO holders meet the AMT.

OBBBA left the exemption amounts at their higher post-2017 levels, which helps. It changed the phaseout instead: the income level where the exemption starts shrinking, and the speed at which it shrinks. Both moved against high earners for 2026.

The three numbers that moved

For a married couple filing jointly in 2026:

The AMT rates themselves are unchanged: 26% on AMT income up to $244,500, and 28% above it.

The 42% band inside the phaseout

When you are inside the phaseout range, each extra dollar of AMT income is taxed at the 28% rate and also removes 50 cents of your exemption, which exposes another 50 cents to tax. Together those push the effective marginal rate near 42%, higher than the headline 28% AMT rate and higher than several ordinary brackets.

This matters most for ISO holders. An exercise that pushes your AMT income into the phaseout band is taxed more than the rate table suggests. The band starts at $1,000,000 of AMT income for joint filers, and a large exercise can put you inside it.

This is an estimate only. Consult a qualified tax or financial advisor for personalized advice.

A worked example

Meet Priya, a staff software engineer at Vantia Robotics, a pre-IPO defense-tech company. She holds 10,000 vested ISOs with a $2 strike and a $22 fair market value. She wants to exercise and hold to start her long-term capital gains and QSBS clocks, so her bargain element is $200,000. Regular tax ignores that $200,000. AMT does not.

Added to her AMT income and taxed at the 26% to 28% AMT rates, that $200,000 slice carries roughly $52,000 to $56,000 of tentative minimum tax. She owes it as AMT to the extent it tops her regular tax on the same income, and since regular tax never counted the spread, most of it becomes a real bill in April.

Now give Priya a partner who also earns well, so the couple already sits at $1,000,000 of AMT income before she exercises. The same $200,000 spread now lands entirely inside the 42% band. The exercise that would have cost her about $52,000 in a lower-income year costs closer to $84,000 once the phaseout claws back the exemption. Same grant, same strike, a different bill driven only by the income she exercised into.

Here is the mental model. AMT is a second tax bill calculated beside your regular one, and you pay whichever comes out higher. For most of the year your regular bill wins. Exercise a large block of ISOs and the AMT bill can jump ahead, so the spread you never "received" in cash still sets what you owe.

Who this hits hardest

Three groups feel the 2026 change most:

Why more ISO holders will owe AMT this year

Three forces compound in 2026. The phaseout threshold dropped, so high earners reach it sooner. The phaseout rate doubled, so the exemption disappears faster once they do. And valuations at many pre-IPO firms have climbed, widening the bargain element on every share exercised.

The practical result: exercises that fit under the AMT line in prior years now cross it. If you are planning an early exercise or an exercise-and-hold to start your long-term capital gains and QSBS clocks, run the 2026 numbers before you commit. You may owe AMT on the same plan that was clear last year.

What to do before December 31

AMT is calculated on the calendar year, which makes timing your strongest lever. A few moves worth pricing out now:

1. Find your crossover. The most useful figure is the largest number of shares you can exercise before AMT begins. Everything up to that point costs you nothing extra; everything past it falls into the 42% band.
2. Split an exercise across two years. Exercising part of your grant in December and part in January spreads the bargain element across two AMT calculations instead of stacking it into one. Splitting a $200,000 spread into two $100,000 exercises can keep each year under the phaseout threshold and preserve the full exemption both times.
3. Mind the phaseout edge. If a planned exercise lands you inside the $1,000,000 band, trimming it to stay below the threshold can save more than the shares are worth in near-term tax.
4. Model the credit. AMT you pay is not always lost (see below), but the timing of recovery affects whether accelerating or delaying makes sense.

How the AMT credit comes back

The AMT you pay is not a penalty. It becomes a minimum tax credit that carries forward with no expiration. In any later year where your regular tax exceeds your tentative minimum tax, the credit releases the difference back to you.

The catch is timing. The credit only returns in years your regular tax runs higher than your AMT, which for many exercisers means after they sell the shares or after a spike in income normalizes. Exercise and hold for years and the cash you paid in AMT sits as a credit the whole time. Plan the exercise around when you expect to recover it, not only the year you trigger it.

For a large exercise the recovery can stretch across several years, because the credit releases a slice at a time. That timing is the real cost of AMT on a long hold, and it is why the size and the year of an exercise matter as much as whether it crosses the AMT line at all.

What did not change

A few things held steady, and they matter:

The mechanics of AMT have not changed. OBBBA moved where the line sits, and in 2026 it sits closer than most ISO holders expect. If you are weighing an exercise, The ISO Exercise Decision: AMT vs. Cash-Flow walks through the full tradeoff, and our Incentive Stock Options guide covers the mechanics.

Common questions

Last updated: July 2026. Reflects the AMT provisions of the One Big Beautiful Bill Act (H.R.1) and IRS Form 6251. This is an estimate only. Consult a qualified tax or financial advisor for personalized advice.