Picture a senior product lead exercising 10,000 ISOs in November. Strike price $15, market price $50. They hold through year-end, because holding is the point. It's what turns the gain into long-term capital gains instead of ordinary income. By April, a tax bill arrives that nobody warned them about: six figures of AMT, federal alone, before the state takes its share. The tax is due now. The one-year holding period doesn't finish until November. Selling shares to pay the bill forfeits the treatment the exercise was for. And if the stock has fallen since November, none of that changes. The AMT is calculated on the $50 the shares were worth at exercise, not what they're worth in April.
That's the AMT problem in one paragraph. This post explains how it works, what triggers it, how the math runs under the 2026 rules, and the credit most people forget to claim, so you can run the number before you exercise.
AMT Isn't an Extra Tax. It's a Parallel One.
The Alternative Minimum Tax is not stacked on top of your regular tax the way the 3.8% Net Investment Income Tax or the 0.9% Medicare surtax are. AMT is a second, parallel calculation. The IRS runs your regular tax, then runs the AMT calculation, and you pay whichever is higher.
So:
Regular tax = $30,000. AMT = $25,000. You pay $30,000.
Regular tax = $30,000. AMT = $35,000. You pay $30,000 in regular tax plus $5,000 in AMT.
The AMT "you owe" on your return is just the gap between the two calculations. That distinction matters later when we get to the credit.
The AMT math differs from regular tax in four places. It adds back certain deductions you took on the regular side. It pulls in income the regular calculation didn't tax. It applies its own exemption (which phases out). And it uses two flat rates, 26% and 28%, instead of the regular brackets.
What Actually Triggers It
For the audience reading this, the answer is almost always one thing: exercising and holding incentive stock options.
When you exercise ISOs and hold the shares past year-end, the bargain element, the spread between the strike price and the fair market value at exercise, gets added to your AMT income. On the regular tax side, that spread is invisible until you sell. On the AMT side, the IRS taxes it the year you exercise. (For the deeper mechanics of how ISO taxation works in both calculations, see the ISO taxation guide.)
Other things can trigger AMT: large amounts of accelerated depreciation, significant tax-exempt interest from private activity bonds, big net operating loss or passive activity loss deductions. But if you're reading about AMT and equity comp, the trigger is almost certainly ISOs.
The Three Numbers That Decide It
Three moving pieces drive the AMT calculation: the add-backs, the exemption, and the rates.
The add-backs. AMT income starts with your regular taxable income, then makes adjustments. The deductions that get added back or reduced include the standard deduction (if you took it), state and local taxes, investment interest expense, certain depreciation, and the net operating loss deduction. The most consequential addition for equity comp: the ISO bargain element described above.
The exemption. Once you have AMT income (AMTI), you subtract an exemption, but only if your income is low enough to qualify. The exemption phases out at higher incomes, and under the 2026 rules it phases out fast.
The 2026 numbers:
For every dollar your AMTI exceeds the phaseout threshold, the exemption is reduced by 50 cents. That's the 2026 phaseout rate. It matters more than it used to. We'll come back to why in a minute.
The rates. Whatever AMT income remains after the exemption gets taxed at two flat rates. The first $244,500 of taxable AMTI is taxed at 26%, or $122,250 if you file separately. Anything above that is taxed at 28%. Long-term capital gains and qualified dividends still get preferential treatment under AMT: they're carved out and taxed at the regular long-term rates, same as on the regular side.
After all that, the IRS compares your tentative minimum tax to your regular tax. If the tentative minimum tax is higher, the difference is the AMT you owe.
The 2026 Change Most Tech Employees Haven't Caught
For about nine years after the Tax Cuts and Jobs Act, AMT was a quiet problem. The exemption was generous, the phaseout started high, and most equity-heavy tech employees could exercise modest ISO lots without crossing into AMT territory. That cushion is mostly gone.
The One Big Beautiful Bill Act made the higher exemptions permanent, which sounds like good news. The catch is what it did to the phaseout. Under prior rules, the exemption phased out at 25 cents per dollar of income above the threshold. Under the new rules, the exemption phases out at 50 cents per dollar, twice as fast, and the phaseout thresholds reset down to $500,000 single and $1,000,000 joint, compared to $626,350 and $1,252,700 in 2025.
What this means in practice: a married couple with combined W-2 income around $700,000 who exercises a meaningful ISO lot is now substantially more likely to lose part or all of the AMT exemption. A single filer in the same situation crosses the threshold even faster. The combined income range where AMT planning matters has gotten wider, and the penalty for ignoring it has gotten sharper.
If you exercised ISOs in 2024 or 2025 and walked away without AMT, that doesn't tell you what 2026 looks like for the same exercise. The math is different now.
What It Costs on 10,000 Shares
Take a senior engineer at a public tech company. Single filer. $400,000 in W-2 wages. In November they exercise 10,000 ISOs at a $15 strike while the stock trades at $50, and hold the shares to start the clock on long-term capital gains treatment. The exercise itself takes $150,000 of cash. That part they planned for.
The bargain element: 10,000 shares × ($50 - $15) = $350,000.
On the regular tax side, nothing happens. No shares were sold, so there's no income to report. On the AMT side, that $350,000 gets added to AMT income. Combined with the $400,000 W-2, AMTI lands at $750,000. The standard deduction you took on the regular side gets added back here, which is why the AMT figure comes right back to wages plus the bargain element.
That's well past the $500,000 phaseout threshold for a single filer. The exemption gets reduced by 50% of $250,000, $125,000. Since the full exemption is only $90,100, it's wiped out completely. All $750,000 of AMTI is exposed to the 26% and 28% rates.
The tentative minimum tax runs roughly: $244,500 × 26% + ($750,000 - $244,500) × 28% = $63,570 + $141,540 = $205,110. The regular tax on $400,000 of W-2 income, after the $16,100 standard deduction and the 2026 brackets, runs about $103,000.
The gap, the AMT bill, is right around $102,000. Federal only. State on top.
What those figures leave out. Everything above is income tax. The 0.9% Additional Medicare Tax also applies to earned income above $200,000 for single filers and $250,000 for joint filers, so the $400,000 salary carries roughly $1,800 more. It's reported separately on Form 8959 and sits outside the AMT comparison, so it doesn't change the $102,000, but it does mean the total federal bill runs higher than the income-tax math alone suggests. One small mercy: the ISO bargain element isn't wages for Medicare purposes, so it adds nothing to that base.
The shares triggered the bill, and selling some of them is the obvious way to pay it. But the one-year clock from exercise doesn't run out until November, so a sale in April is a disqualifying disposition: ordinary income on the spread, and the long-term treatment gone on every share sold. The AMT is locked in either way by then. Selling before December 31 of the exercise year is the move that pulls the bargain element back out of the AMT calculation entirely, and that timing question is the whole of the ISO bail-out strategy. If the shares are genuinely illiquid, private company, no tender, no secondary, the trade gets worse: the bill is real and the only asset that could cover it can't be sold at all.
The Credit Most People Forget to Claim
Here's the redemption arc, if there is one. AMT from ISO exercise is a deferral item, the IRS's term for a difference that reverses over time. The bargain element you paid AMT on in the year of exercise becomes part of your basis when you eventually sell. So on the regular tax side, your capital gain at sale is smaller than it would have been without the AMT basis adjustment.
To prevent double-taxation across the two calculations, the IRS lets you claim a credit in future years equal to the AMT you paid on deferral items. The credit shows up on Form 8801, and you apply it in any year where your regular tax exceeds your tentative minimum tax, usually any year you're not exercising fresh ISOs.
Three things to know:
The credit carries forward indefinitely. No expiration. You can chip away at a six-figure AMT credit over a decade if that's what it takes to use it up.
You have to file Form 8801 every year to track it. Skip a year and the credit doesn't vanish, but you've created bookkeeping debt for yourself and your CPA. Worse, people sometimes change CPAs, lose records, and forget the credit exists entirely.
The credit can only offset regular tax: it can't generate a refund. That means the years to claim it are years when your tentative minimum tax is low relative to your regular tax. Which is most years, for most people, unless you're stacking ISO exercises.
This is the easiest six figures in the tax code to lose track of, especially across a CPA change. It's money sitting in IRS bookkeeping that belongs to you and is recoverable with a form.
Where AMT Lives in a Real Plan
The AMT calculation runs in isolation on Form 6251. The planning doesn't.
A decision to exercise ISOs interacts with cash flow (do you have liquidity to cover the bill if AMT triggers?), with state tax (California treats ISO exercise differently than most states; residency at exercise matters), with multi-year tax projection (does it make sense to exercise smaller lots across multiple years to stay under the phaseout threshold?), with concentrated position management (you've now got shares with split AMT and regular tax basis you have to track for decades), and with estate planning (the credit is a tax attribute that doesn't transfer cleanly at death).
That's the part most ISO calculators don't show. A single exercise decision ripples through five other planning areas, and the real question is whether the cost of that ripple is smaller than the cost of waiting another year.
You Can't Always Avoid It. You Can Always Plan Around It.
For most equity-heavy tech employees, AMT isn't a tax to dodge. It's a cost to weigh. Exercising ISOs and holding for the long-term capital gains treatment is often the right financial move even when AMT is triggered: the tax savings on the eventual sale can be larger than the AMT bill at exercise, especially if you can use the credit efficiently afterward.
Being surprised by it is the actual problem. The April version of you would much rather have known about the bill before the exercise, when there was still time to size it, run the projection, build a liquidity plan, and decide whether the trade was worth making at all.