Alternative Minimum Tax (AMT): What It Is, Who Pays It, and How ISOs Trigger It

Alternative Minimum Tax (AMT) is a parallel tax system in the United States that runs alongside the regular federal income tax. It was designed to ensure that high-income taxpayers who benefit from certain deductions, credits, and exclusions still pay a minimum amount of tax. For tech employees, the AMT is most relevant because exercising Incentive Stock Options (ISOs) can trigger a significant AMT bill — even though ISO exercises are not taxed under the regular income tax system.

This guide explains what the AMT is, how it works, current exemption amounts and rates, the connection to ISOs, and how the AMT credit carryforward can help you recover AMT paid in future years.

Why the AMT Exists

Congress created the AMT in 1969 after discovering that 155 high-income individuals paid zero federal income tax by stacking deductions and exclusions. The AMT acts as a floor — a minimum tax that applies when your regular tax liability falls below a certain threshold after accounting for "preference items" and "adjustments."

In practice, the AMT primarily affects:

• Employees who exercise ISOs with a large spread
• High earners in states with significant state/local tax (SALT) deductions
• Individuals with large miscellaneous deductions

For tech employees, ISO exercises are by far the most common AMT trigger. The spread between your strike price and the fair market value at exercise (the "bargain element") is an AMT preference item, even though it is not taxed under the regular system.

How the AMT Works: Step by Step

The AMT calculation runs in parallel with your regular tax. You pay whichever is higher.

Step 1: Calculate Alternative Minimum Taxable Income (AMTI)

Start with your regular taxable income and add back certain deductions and preference items:

Step 2: Subtract the AMT Exemption

The AMT exemption shields a portion of your AMTI from the AMT. For 2025:

The exemption phases out at 25 cents per dollar of AMTI above the phase-out threshold. This means the exemption is completely eliminated at $978,750 for single filers ($88,100 / 0.25 + $626,350) and $1,800,700 for MFJ.

Step 3: Apply AMT Tax Rates

The AMT has its own rate structure — simpler than regular tax but with only two brackets:

(For MFS, the 28% rate applies above $124,150.)

Step 4: Compare to Regular Tax

• If AMT > Regular Tax: You pay AMT (the difference is your "AMT liability")
• If Regular Tax > AMT: You pay regular tax and owe no AMT

How ISO Exercises Trigger AMT

When you exercise an Incentive Stock Option, the spread (FMV at exercise minus strike price) is an AMT preference item. It is added to your income for AMT purposes on Form 6251, Line 2i, even though it is not included in your regular taxable income.

Worked Example: ISO Exercise Triggering AMT

Regular tax calculation:

• Taxable income: $200,000 (ISO spread not included)
• Regular federal tax: ~$35,500

AMT calculation:

• AMTI: $200,000 + $90,000 = $290,000
• AMT exemption: $88,100 (assuming single, no phase-out)
• AMTI after exemption: $201,900
• Tentative minimum tax: $201,900 x 26% = $52,494
• AMT liability: $52,494 - $35,500 = $16,994

In this example, the ISO exercise triggers an additional $16,994 in AMT — a tax bill on income you have not actually received in cash (you exercised the options but have not sold the shares).

This is exactly the kind of scenario our ISO AMT calculator helps you model before you exercise.

AMT Exemption Phase-Out

The AMT exemption is not available to everyone. It phases out for high-income taxpayers:

For a single filer in 2025 with AMTI of $700,000:

• AMTI above phase-out threshold: $700,000 - $626,350 = $73,650
• Exemption reduction: $73,650 x 25% = $18,413
• Remaining exemption: $88,100 - $18,413 = $69,688

If your AMTI is high enough (above $978,750 for single filers), the exemption is completely eliminated and the full AMT rate applies to your entire AMTI.

AMT Credit Carryforward

Here is the good news: AMT you pay due to ISO exercises is not lost forever. It generates an AMT credit (reported on Form 8801) that you can use to reduce your regular tax in future years.

The AMT credit works as follows:

1. You pay AMT in the exercise year (e.g., $16,994 in the example above)
2. In subsequent years, if your regular tax exceeds your tentative minimum tax, you can apply the credit
3. The credit carries forward indefinitely until fully used

When does the credit become usable? Typically when you sell the ISO shares (which removes the preference item) or when your income is lower in a future year. Many employees recover their full AMT credit within 1-3 years after the exercise year.

California State AMT

California has its own separate Alternative Minimum Tax, calculated on Form 540 Schedule P (Alternative Minimum Tax and Credit Limitations). If you live and work in California — as many tech employees do — you may face both federal and California AMT simultaneously on the same ISO exercise.

Key differences from federal AMT:

Worked example (same $200K salary + $90K ISO spread):

A Bay Area employee with a $200,000 salary who exercises ISOs with a $90,000 spread faces both federal AMT (~$16,994 as calculated above) and California AMT. The California calculation:

• California AMTI: approximately $290,000 (salary + ISO spread, with California-specific adjustments)
• Less California AMT exemption: ~$117,000
• California tentative minimum tax: ~$173,000 x 7% = ~$12,110
• California regular tax on $200K salary: approximately $11,000
• California AMT owed: approximately $1,110

Combined federal + state AMT: $16,994 + $1,110 = approximately $18,104. The state AMT is smaller than federal, but it adds up — and California's AMT credit carryforward rules are not as generous as the federal system's.

For California-specific tax planning, see our California income tax guide.

TCJA and AMT History

The Tax Cuts and Jobs Act (TCJA) of 2017 dramatically changed who is affected by AMT:

• Before TCJA (2017 and earlier): The AMT exemption was approximately $54,300 for single filers. Millions of upper-middle-income taxpayers owed AMT because they claimed large state and local tax (SALT) deductions, personal exemptions, and miscellaneous itemized deductions — all of which were added back for AMT purposes.
• After TCJA (2018-2025): The exemption was raised to $81,100+ (single) and indexed annually — reaching $88,100 in 2025. The $10,000 SALT deduction cap removed one of the biggest AMT triggers. Personal exemptions were eliminated. The result: approximately 95% fewer taxpayers owe AMT compared to pre-TCJA years.
• 2026 and beyond: Many TCJA provisions are scheduled to sunset after 2025. If Congress does not act to extend them, exemptions could revert to approximately $60,000 levels (inflation-adjusted pre-TCJA amounts), and the SALT cap may be lifted. This would dramatically increase the number of AMT-affected taxpayers and make ISO exercise planning even more critical.

For current and projected future tax brackets, see our 2026 federal tax brackets guide.

AMT and Estimated Tax Payments

AMT creates a tax liability with zero withholding. Your employer does not withhold for AMT on ISO exercises — unlike RSU vesting, where supplemental withholding is automatic. You must self-calculate your AMT exposure and pay quarterly estimated taxes.

• Underpayment penalty: If you owe more than $1,000 at filing time and did not make sufficient estimated payments during the year, the IRS charges an underpayment penalty at approximately 8% annualized interest (2025 rate). This penalty is calculated quarter by quarter.
• Safe harbor rule: You can avoid the penalty entirely by paying at least 100% of your prior year's total tax liability through withholding plus estimated payments (110% if your AGI exceeds $150,000). This is often the easiest approach — calculate last year's total tax, confirm your W-2 withholding covers most of it, and make estimated payments for the rest.
• Quarterly deadlines: April 15, June 15, September 15, and January 15 of the following year. If you exercise ISOs in Q1, your first estimated payment is due April 15.

For a complete walkthrough of estimated tax payments after an ISO exercise, see our estimated taxes on ISO exercise guide and quarterly estimated tax guide.

Who Is Most at Risk for AMT?

Post-TCJA, the AMT affects a much narrower population than it did before 2018. The typical AMT risk profile for tech employees:

• Income range: $150,000-$500,000. High enough that ISO spreads create a meaningful AMT adjustment, but not so high that regular tax already exceeds the tentative minimum tax at all exercise levels.
• Equity type: Incentive Stock Options (ISOs). These are the only common AMT trigger for W-2 employees in the post-TCJA era. RSUs, NSOs, and restricted stock do not create AMT preference items.
• State: California and New York are the highest-risk states because they have their own state-level AMT in addition to federal. Washington and Texas residents avoid state AMT entirely (no state income tax).
• Life event: Pre-IPO or pre-acquisition exercise of large ISO grants. The spread tends to be largest when you exercise close to a liquidity event, because the 409A valuation has been climbing with each funding round.

If you match two or more of these factors, you should model your AMT exposure before exercising any ISOs. Our ISO AMT Calculator finds the maximum number of shares you can exercise without triggering AMT — the "AMT-free exercise limit."

Strategies to Minimize AMT

1. Limit annual ISO exercises — Exercise only enough shares to stay below the AMT crossover point. Our ISO AMT calculator finds this exact number for your situation.

2. Spread exercises across multiple tax years — Instead of exercising all your vested options at once, exercise in batches over 2-3 years to keep each year's spread below the AMT trigger.

3. Time exercises in low-income years — If you have a year with lower W-2 income (e.g., between jobs, sabbatical, reduced hours), that is an ideal time to exercise ISOs because the lower base income gives you more room before hitting AMT.

4. Same-day sale (disqualifying disposition) — Exercising and immediately selling converts the spread to ordinary income for regular tax purposes, which eliminates the AMT preference item. You lose the potential for long-term capital gains treatment, but you also avoid AMT entirely. Learn more about disqualifying dispositions.

5. Monitor the AMT crossover point — The point where AMT equals regular tax is your maximum AMT-free exercise amount. Our calculator finds this using a binary search algorithm — see our exercise planning guide.

Frequently Asked Questions

Who has to pay AMT?

Anyone whose tentative minimum tax (calculated under AMT rules) exceeds their regular tax. For most tech employees, the primary trigger is exercising ISOs with a significant spread. High-income earners in high-tax states can also be affected due to SALT deduction limitations.

Is AMT an extra tax on top of regular tax?

No. You pay the greater of regular tax or AMT. The AMT liability on your return is only the difference between AMT and regular tax. Think of it as a floor — your tax cannot go below the AMT amount, but you do not pay both.

Can I get AMT money back?

Yes. AMT paid due to "deferral items" like ISO exercises generates an AMT credit carryforward (Form 8801). You can use this credit to reduce your regular tax in future years. The credit carries forward indefinitely.

How do I know if I owe AMT before I file?

Run the numbers before you exercise ISOs. Use our ISO AMT calculator to model exactly how many shares you can exercise before triggering AMT. You can also use the simplified Form 6251 walkthrough to estimate manually.

Does AMT apply to RSUs?

No. RSUs are taxed as ordinary income at vesting under both the regular tax and AMT systems. There is no AMT preference item for RSU income. AMT is primarily a concern for ISOs and certain other tax preference items.