Alternative Minimum Tax (AMT) Primer
A parallel federal tax system designed to ensure high-income filers cannot zero out their tax with deductions. Mostly defanged by the 2017 TCJA but still relevant in narrow scenarios.
The short answer
The AMT is a parallel tax calculation - you compute your tax both ways and pay the higher number. After the 2017 TCJA raised the exemption, most W-2 earners no longer owe it. The big remaining trigger is exercising incentive stock options (ISOs) with a large paper spread.
2026 tax year. Long-term gains and qualified dividends keep their 0/15/20% rates inside AMT.
The Alternative Minimum Tax is a parallel federal income tax computation. Calculate your tax under the regular system, calculate it again under AMT rules, and pay whichever number is higher. The AMT system disallows many regular deductions (state and local taxes, SALT, being the main one), uses different brackets, and applies a large exemption. For most W-2 wage earners, AMT no longer applies after the 2017 reforms, but for a narrow set of filers (especially those exercising incentive stock options), it can still produce a six-figure surprise tax bill.
What AMT Actually Is
Originally enacted in 1969 as a “millionaire's minimum tax” to prevent zero-tax returns by high-income filers using shelters, the AMT crept down over the decades. By 2017, it hit roughly 5 million households because the exemption was not inflation-indexed and bracket creep gradually pulled middle-income filers into its net. The 2017 Tax Cuts and Jobs Act (TCJA) raised the exemption substantially and began indexing it, dropping AMT filers to about 200,000 households today.
Mechanically, the AMT calculation:
- Start with your regular taxable income
- Add back AMT “preference items” (most notably the SALT deduction, ISO exercise spread, certain depreciation differences)
- Subtract the AMT exemption
- Apply the AMT rate schedule (26% / 28%)
- Compare to regular tax, pay whichever is higher
2026 AMT Numbers at a Glance
Every dollar amount on the AMT side is now indexed annually. For 2026:
| Parameter | Single | Married Jointly | Married Separately |
|---|---|---|---|
| AMT exemption amount | $87,350 | $135,650 | $67,825 |
| Exemption phaseout begins | $626,350 | $1,252,700 | $626,350 |
| Exemption fully phased out | $975,750 | $1,795,300 | $897,650 |
| 26% AMT rate ceiling (AMTI) | $239,100 | $239,100 | $119,550 |
| 28% AMT rate floor (AMTI) | Above $239,100 | Above $239,100 | Above $119,550 |
Long-term capital gains and qualified dividends in AMT use the same preferential 0%/15%/20% rates as regular tax, they are not penalized in the parallel system. That preserves capital-gains favoritism even for AMT filers.
Who Actually Owes AMT in 2026
Three patterns trigger AMT after the TCJA reforms. If none of these match your situation, you almost certainly do not owe AMT in 2026:
Pattern 1: Large Incentive Stock Option Exercise with High Spread
Exercising ISOs creates AMT preference income equal to the spread (FMV at exercise minus strike price) multiplied by shares exercised. A founder or early employee exercising 50,000 ISOs at a $5 strike when the FMV is $50 generates $2.25 million of AMT preference income, almost certainly triggering AMT. The cash tax can be staggering, even though no shares have actually been sold and no liquidity has occurred.
This is the #1 AMT scenario in modern Silicon Valley. A typical pre-IPO senior engineer with vested ISOs faces a hard choice: exercise early (when spread is small but cash outlay is upfront and long-term illiquid), exercise gradually each year staying within AMT exemption, or hold until IPO/sale and take ordinary-income treatment via a same-day sale.
Pattern 2: Very High Income with Large State-Tax Deduction Stacks
A New York or California filer earning $1M+ who itemizes can still see AMT bite if multiple AMT-disallowed items pile up at once: large SALT (now capped at $40,000 for 2025-2029 under recent legislation), miscellaneous itemized deductions (mostly disallowed under TCJA anyway), or large depletion deductions from oil-and-gas pass-throughs.
Pattern 3: Pass-Through Business Owners with Depreciation Differentials
Some pass-through business owners, particularly in real estate, oil and gas, and equipment-heavy industries, accumulate large depreciation differentials between regular and AMT systems. The AMT side requires Alternative Depreciation System (ADS) treatment, which is slower than MACRS used in regular tax. The cumulative gap can push AMTI above regular taxable income enough to trigger AMT.
The ISO Exercise Trap, in Detail
Worth a deep look because it is so common and so painful. The mechanics:
- An employee receives an ISO grant with a $1 strike price when the company is small.
- Five years later, the company's 409A valuation (a private-company FMV) has climbed to $40 per share.
- The employee exercises 10,000 ISOs to start the long-term holding period before an expected IPO. Cash outlay: $10,000 (10K × $1 strike). The shares are now worth $400,000 on paper.
- The AMT preference income equals (FMV − strike) × shares = ($40 − $1) × 10,000 = $390,000.
- This $390,000 of phantom income triggers AMT, perhaps $80,000-$100,000 of additional tax owed at filing time, in cash, with no shares sold.
- If the company never IPOs or fails, the AMT credit generated may take many years to recover, and in worst-case scenarios, may never be fully recovered.
The standard mitigation strategies are well-known to anyone who has worked in startups for more than a year: exercise early when the spread is small (right after grant, ideally before the 409A valuation has appreciated), spread exercises across multiple tax years to stay below the AMT exemption ceiling, or do a same-day sale at IPO and accept the ordinary-income treatment.
The AMT Credit Carryforward
Here is the slim consolation: if you pay AMT in a year, the difference between regular tax and AMT becomes an AMT credit (Form 8801) that can offset regular tax in future years, but only to the extent your future regular tax exceeds your future AMT.
For ISO exercisers, this typically means the credit can only be drawn down once the underlying shares are sold and the regular-tax basis adjusts. The basis for regular tax is the original strike price; for AMT it includes the spread paid as AMT income. So when shares are eventually sold, regular-tax basis is lower and regular-tax gain is higher, but AMT-basis is higher so AMT gain is lower. The arithmetic difference is what releases the credit.
In practice, full credit recovery often takes 5-15 years after a major ISO exercise, depending on company outcome and the holder's post-exercise income trajectory. For employees at companies that never reach liquidity, the credit may carry forward indefinitely without ever being usable.
How to Tell If You Might Owe AMT
Three quick screens will catch nearly every modern AMT case:
- Did you exercise ISOs this year, with a spread (FMV − strike) of more than about $40,000? You probably owe AMT, calculate it.
- Is your taxable income above $300,000 with significant pre-tax SALT addbacks, ISOs, or depreciation? Worth running the AMT computation.
- Did you owe AMT last year? Your AMT credit carryforward can sometimes flip the calculation in current year.
Most modern tax software (TurboTax, H&R Block, FreeTaxUSA, professional packages) automatically computes both systems and reports nothing if AMT does not apply. The main risk is for filers preparing returns by hand or with older software, and for ISO exercisers who do not realize their grant created any AMT exposure.
FAQ
Does the standard deduction trigger AMT?
No. Standard deduction is allowed in both regular tax and AMT, so it does not create a preference item. Itemized SALT deductions are the more common AMT trigger, and even those have been muted by the SALT cap.
If I am a typical W-2 worker earning under $400K, do I need to worry about AMT?
Very unlikely. Post-TCJA, the AMT exemption is high enough that a typical wage earner with no ISOs, no large depreciation, and no exotic deductions will not owe AMT. If your tax software does not flag AMT after running a complete return, you almost certainly do not owe it.
What is “AMTI” that I see on Form 6251?
Alternative Minimum Taxable Income. It is your regular taxable income with AMT preference items added back and AMT-disallowed deductions removed, before subtracting the AMT exemption. The 26%/28% rates apply to AMTI minus exemption.
Can a single ISO exercise really push me from no AMT to a $100K bill?
Yes, easily. A modest 10,000-share ISO exercise with a $40 spread per share creates $400,000 of AMT preference income, enough to push a typical $200K wage earner from $0 AMT to $80,000+ in additional tax. The math is unforgiving precisely because ISO spread is added directly to AMTI without offset by the ISO exercise itself being a real cash event.
Sources
- IRS Revenue Procedure 2025-32 - 2026 AMT exemption and thresholds
- Tax Cuts and Jobs Act of 2017, TCJA AMT reforms
- IRC §55-59, Alternative Minimum Tax statutes
- IRS Form 6251, Alternative Minimum Tax, Individuals
- IRS Form 8801, Credit for Prior Year Minimum Tax