What is AMT Calculator for ISO Exercises?
Free AMT calculator for ISO exercises. Estimate the Alternative Minimum Tax on incentive stock options — AMTI, exemption with phaseout, and the AMT crossover point. No signup.
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Free AMT Calculator for ISO Exercises
Estimate the Alternative Minimum Tax when you exercise and hold Incentive Stock Options. Enter your filing status, regular taxable income, and ISO grant details to see the bargain element, AMTI, the AMT exemption with phaseout, tentative minimum tax, AMT owed, and the AMT crossover — the largest exercise that still triggers $0 of AMT.
Your ISO exercise
2025 AMT rulesYour taxable income after deductions, before the ISO exercise.
The 409A or market price on the exercise date.
Private-activity bond interest, depreciation adjustments, etc. Leave at $0 if none.
Try a scenario
Estimated AMT on this exercise
$0
Extra federal tax owed by April 15 of next year — in cash, before you have sold any shares.
Approximate AMT crossover
At this income and price, you could exercise about 1,279 shares ($57,575 of bargain element) before AMT begins.
Estimated AMT on this exercise
$0
AMT crossover: about 1,279 shares before AMT begins.
⚠️ AMT is a cash hit now, even though you haven't sold. AMT paid on an ISO exercise often becomes an AMT credit (Form 8801) you can recover in future years when regular tax exceeds tentative minimum tax — but recovery can take many years, and some exercisers have lost their upside paying AMT on shares that later fell in value. State AMT (CA, CO, MN, IA and others) is not modeled here. Verify with a CPA before exercising a significant ISO position.
Estimated AMT
$0
📐 Open methodology, sources & limitations
Formula
bargain element = (FMV − strike) × ISO shares
AMTI = regular taxable income + bargain element + other preferences
exemption = base exemption − 25% × max(0, AMTI − phaseout threshold)
AMT base = max(0, AMTI − exemption)
Tentative Minimum Tax = 26% × min(AMT base, breakpoint)
+ 28% × max(0, AMT base − breakpoint)
AMT owed = max(0, Tentative Minimum Tax − regular income tax)
Crossover: the largest bargain element for which AMT owed is still $0,
found by binary search (AMT owed rises monotonically with the bargain element).Assumptions
- 2025 AMT exemptions: $88,100 single / head of household, $137,000 married filing jointly, $68,500 married filing separately.
- Exemption phaseout begins at AMTI of $626,350 (single/HoH/MFS) and $1,252,700 (MFJ), reducing the exemption by 25 cents per dollar over the threshold.
- AMT rate is 26% on the AMT base up to $239,100 ($119,550 MFS) and 28% above.
- Regular tax is computed by a 2025 ordinary-bracket walk on the regular taxable income entered — capital gains are not separately rate-stacked.
- The bargain element is treated as a held position (no same-year disqualifying disposition).
Sources
- IRC §55 — Alternative Minimum Tax imposed — §55
- IRC §56(b)(3) — ISO exercise as an AMT adjustment — §56(b)(3)
- IRC §57 — Items of tax preference — §57
- IRS Form 6251 Instructions — Alternative Minimum Tax for Individuals
This tool does NOT model:
- AMT credit carryforward (Form 8801) recoverable in later years
- ISO disqualifying dispositions, which convert the spread to ordinary income
- State AMT (California, Colorado, Minnesota, Iowa and others)
- Capital gains taxed at preferential rates within the AMT system
- Section 1202 QSBS exclusion interactions with AMT
- Tax years other than 2025 — exemptions and thresholds adjust annually
Last reviewed: 2026-05-20 · Tax year modeled: 2025
This methodology section exists so you can verify the math. We show our formulas because you deserve to know how a number was calculated. This is calculation transparency, not financial advice.
Why ISOs trigger AMT
When you exercise an Incentive Stock Option and hold the shares, no regular income tax is due — that is the tax advantage of an ISO. But the bargain element (the spread between the fair market value and your strike price, times the number of shares) is an AMT preference item under IRC § 56(b)(3). It is added to your income for the parallel Alternative Minimum Tax calculation, even though you have not sold a single share and have received no cash.
You then pay whichever is higher: your regular income tax, or the tentative minimum tax. The difference — when AMT is higher — is the AMT owed, and it is due in cash by the filing deadline. For an employee exercising a large ISO grant in a single year, that bill can run into the tens of thousands of dollars.
The AMT credit — and why it isn't a free pass
AMT paid because of an ISO exercise generally becomes a minimum tax credit(Form 8801) that you can use in future years when your regular tax exceeds your tentative minimum tax. In theory the AMT is “recoverable.” In practice, recovery can take many years, and it does nothing to help with the immediate cash-flow problem. The classic cautionary tale is the dot-com crash: employees exercised and held ISOs, owed AMT on a large paper spread, then watched the stock collapse — leaving them with a real tax bill on value that had evaporated.
Using the AMT crossover
The crossover is the largest bargain element you can realize in a year before AMT begins. Below the crossover, your tentative minimum tax stays at or under your regular tax and you owe $0 of AMT. Many employees use this number to exercise in tranches — exercising up to the crossover each year to move shares into the long-term holding clock without ever triggering AMT.
- Exercise early in the year. You then have until December to decide whether to do a same-year sale (a disqualifying disposition) and avoid the AMT entirely.
- Consider a partial same-year sale. Selling some shares in the year of exercise can fund the AMT bill on the shares you keep.
- Have an exit plan before you exercise and hold. Exercising and holding ISOs is a leveraged bet on your company's stock plus a tax bill. If the stock falls, the AMT bill does not.
- This is an estimate, not advice. AMT interacts with the credit carryforward, state AMT, capital-gains stacking and your full return. Confirm the numbers with a CPA before exercising a significant position.
Frequently Asked Questions
What is the Alternative Minimum Tax?+
The AMT is a parallel federal tax system that recomputes your income with certain deductions and exclusions removed, applies a separate exemption, and taxes the result at 26% or 28%. You pay whichever is higher — your regular tax or the tentative minimum tax.
Why do ISOs trigger AMT?+
When you exercise an Incentive Stock Option and hold the shares, the bargain element (FMV minus strike, times shares) is an AMT preference item under IRC §56(b)(3). It is added to income for the AMT calculation even though you have not sold the shares or received any cash.
How is AMT different from regular tax?+
Regular tax uses the ordinary brackets and all normal deductions. AMT uses a flat 26%/28% rate, a separate exemption that phases out at high income, and adds back preference items like the ISO bargain element. AMT owed is the amount by which the tentative minimum tax exceeds your regular tax.
What is the AMT credit (Form 8801)?+
AMT paid because of an ISO exercise generally becomes a minimum tax credit you can claim on Form 8801 in future years when your regular tax exceeds your tentative minimum tax. It can be recovered over time — but recovery can take many years and does not help with the immediate cash bill.
Does a same-day sale of ISOs avoid AMT?+
Yes. Selling ISO shares in the same year you exercise is a disqualifying disposition: the spread becomes ordinary income (like an NQSO) and there is no AMT preference. You lose the favorable ISO holding treatment, but you avoid the AMT cash crunch.
What is the AMT crossover point?+
The crossover is the largest bargain element — and therefore the largest number of shares — you can exercise in a year before AMT begins. Below it, the tentative minimum tax stays at or under your regular tax, so AMT owed is $0. Many people exercise in tranches up to the crossover each year.
Do vested but unexercised options trigger AMT?+
No. AMT is triggered by the exercise of an ISO while holding the shares, not by vesting. Options you hold but have not exercised create no AMT preference.
How does the AMT exemption phaseout work?+
The AMT exemption is reduced by 25 cents for every dollar of AMTI above the threshold ($626,350 single/HoH, $1,252,700 MFJ for 2025). A large ISO exercise can push AMTI into the phaseout range, shrinking the exemption and increasing AMT.
Does AMT apply at the state level?+
Some states have their own AMT — California, Colorado, Minnesota and Iowa among them — and the rules differ from federal. This calculator models federal AMT only. Check your state if you are exercising a large ISO position.
How do I report AMT on my tax return?+
AMT is computed on IRS Form 6251, Alternative Minimum Tax — Individuals. The ISO bargain element is entered as an adjustment. Any AMT credit carried to future years is tracked on Form 8801.
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