ISO Exercises and the AMT: The Tax Bill on Gains You Haven't Cashed

Exercise 10,000 incentive stock options at a $2 strike when the shares are worth $22, hold them, and sell nothing. You have zero cash in hand, and a $200,000 AMT preference item that can generate a tax bill north of $50,000 due the following April. That is the trap in ISOs: the alternative minimum tax reaches a gain you have not cashed.

This is the most expensive surprise I see in employee-equity work. The person did everything the internet told them (exercise early, hold for the long-term rate) and never modeled the AMT. Then the stock drops, and they owe tax on a paper gain that no longer exists.

Why does exercising ISOs trigger AMT if I didn't sell?

Because §56(b)(3) treats the spread at exercise as income for AMT purposes even though it's excluded from regular taxable income. That spread, the "bargain element," is the fair market value at exercise minus your strike price, multiplied by shares exercised.

For regular tax, exercising an ISO and holding is a non-event. You report nothing on your Form 1040 in the year of exercise. For AMT, §56(b)(3) removes that favorable treatment: the bargain element becomes a positive adjustment on Form 6251. You compute tax two ways, regular and AMT, and pay whichever is higher.

Using the example above:

• Shares exercised: 10,000
• FMV at exercise: $22
• Strike: $2
• Bargain element (AMT preference): 10,000 × ($22 − $2) = $200,000

That $200,000 gets added to your alternative minimum taxable income even though you sold nothing and received no cash.

How much AMT will an ISO exercise actually cost?

The AMT rate is 26% on the AMT base up to a breakpoint and 28% above it (§55(b)(1)). For 2026, the 28% rate applies once AMTI in excess of the exemption passes $244,500 ($122,250 if married filing separately), per the annual inflation adjustment under §55(d).

But the marginal cost of an ISO exercise depends heavily on the AMT exemption and its phase-out, and 2026 changed the phase-out by statute, not just by indexing. The exemption for 2026 is $90,100 for single filers and $140,200 for married filing jointly. Under the One Big Beautiful Bill Act, beginning in 2026 the phase-out thresholds reset down to $500,000 of AMTI for single filers and $1,000,000 for joint filers, and the phase-out rate doubled: you now lose 50 cents of exemption for every dollar of AMTI above the threshold, instead of 25 cents. Far more option exercisers hit the phase-out under the new thresholds, and it bites twice as hard when they do.

Inside the phase-out zone, each dollar of bargain element does double damage: it adds a dollar to your AMT base directly and strips away another 50 cents of exemption, so it is taxed as if it were $1.50. The effective marginal cost reaches up to 39% at the 26% rate and 42% at the 28% rate (26% and 28% multiplied by 1.5), well above the headline AMT rates.

Rough math on the $200,000 preference, assuming the exercise pushes a taxpayer well into AMT: 26% to 28% of the spread, or roughly $52,000 to $56,000. And that is the friendly case. Stack a $200,000 bargain element on top of a healthy professional income and a single filer can plausibly cross $500,000 of AMTI, at which point every additional dollar of spread in the phase-out zone costs up to 39 to 42 cents rather than 26 to 28, and the bill climbs meaningfully past the simple estimate.

The practical takeaway: model it before you exercise. The tax is not a percentage of a nice round "gain"; it's the difference between two full tax computations, and the exemption phase-out makes it sharply non-linear. Confirm the current-year figures against the Form 6251 instructions, since the exemption and breakpoint adjust annually and the new phase-out thresholds are indexed going forward.

What happens to the AMT I pay? Do I ever get it back?

Yes, partially and over time, through the AMT credit under §53. AMT paid on an ISO exercise is generally a "timing" item, not a permanent tax, because it creates a minimum tax credit you carry forward and use in future years when your regular tax exceeds your tentative minimum tax.

Two things people misunderstand about the credit:

1. It's not a refund. The §53 credit only reduces regular tax in a year where regular tax exceeds tentative minimum tax. If you stay in AMT, you can carry it for years without using much of it.
2. Your AMT basis differs from your regular basis. Because you paid AMT on the spread, your basis in the shares for AMT purposes is the FMV at exercise, while your regular-tax basis stays at the strike price. When you sell, this gap unwinds: the AMT gain is smaller than the regular gain, which is precisely how the credit gets recovered. Track both bases. A recurring failure mode is the taxpayer who paid $50,000 of AMT and never claimed the credit on sale because nobody tracked the dual basis.

What if I sell the shares in the same year I exercise?

Selling in the same calendar year as exercise creates a disqualifying disposition, which eliminates the AMT preference entirely for that exercise. Under §421 and §422, a qualifying disposition requires holding the shares more than two years from grant and more than one year from exercise. Break either holding period and you have a disqualifying disposition.

The tradeoff:

	Hold (qualifying)	Sell same year (disqualifying)
Regular tax at exercise	None	Ordinary income on the spread
AMT preference	Full bargain element	None (no AMT adjustment)
Gain character on sale	Long-term capital gain	Ordinary + short-term
Cash to pay tax	None from the shares	Proceeds cover the tax

A same-year sale converts the spread to ordinary income (you lose the long-term capital-gains rate), but you also avoid the AMT problem and you have cash to pay the bill. When the stock is volatile or you can't fund the AMT out of pocket, the disqualifying disposition is often the more defensible move. This is a facts-and-circumstances call, and it depends on your other income and state; talk it through before December 31.

How do I keep the AMT hit small when I exercise?

The core lever is controlling how much bargain element lands in a single tax year. A few patterns that work in practice:

• Exercise-and-hold up to your AMT "crossover." There's a quantity of shares you can exercise each year before regular tax and tentative minimum tax diverge. Model that break-even on Form 6251 and exercise up to it annually, spreading the preference across multiple years. With the phase-out thresholds now at $500,000 and $1,000,000, staying under the phase-out is itself a planning target for high earners.
• Exercise early when the spread is small. If FMV is close to your strike (soon after grant, or right after a 409A valuation you believe is low), the bargain element is small, so the AMT preference is small. This is where an 83(b)-style early exercise of unvested ISOs can help, though the rules are technical; get it reviewed.
• Sell enough to fund the tax. A partial same-year sale (disqualifying on those shares) can generate cash to pay AMT on the shares you hold.
• Watch the state. Some states have their own AMT or conform to the federal preference; California, for example, has a state AMT. Multistate and residency facts change the answer.

What's the worst-case scenario, and how do I avoid it?

The worst case is paying AMT on a spread that evaporates. You exercise at $22 FMV, owe roughly $50,000 of AMT, the company's value craters to $3, and you're holding illiquid shares plus a tax bill on a gain that's gone.

Guardrails:

• Never exercise-and-hold more than you can afford to pay the AMT on in cash.
• Model the exercise on a draft Form 6251 before you click "exercise," not in April.
• If the stock is private and illiquid, weigh whether locking up capital and paying phantom tax is worth the long-term-gains rate at all.
• Keep records of your dual basis so you actually recover the §53 credit on sale.

Equity comp is one of the few areas where the tax decision has to be made before year-end and can't be fixed on the return. Run the numbers with your advisor, and confirm every threshold above against the current-year Form 6251 instructions, because these amounts adjust annually, the 2026 law change moved the phase-out goalposts, and the facts of your situation and state control the outcome.

Sources

• IRC §55: alternative minimum tax; rates and exemption
• IRC §55(d): AMT exemption amounts and phase-out thresholds, as amended by the One Big Beautiful Bill Act (2026 thresholds and 50% phase-out rate)
• IRC §56(b)(3): treatment of incentive stock options for AMT
• IRC §53: minimum tax credit
• IRC §421 and §422: statutory (incentive) stock options and holding-period requirements
• Rev. Proc. 2025-32: 2026 inflation adjustments (AMT exemption and 28% breakpoint)
• IRS Form 6251 and instructions: Alternative Minimum Tax, Individuals