Alternative Minimum Tax (AMT)

The Alternative Minimum Tax (AMT) is a parallel federal income tax system enacted in 1969 after Congress discovered that 155 high-income taxpayers paid zero federal income tax by combining multiple legal deductions. The AMT runs alongside the regular tax system — you calculate your tax liability under both systems and pay whichever amount is higher.

The AMT uses a broader income base (called Alternative Minimum Taxable Income, or AMTI) that adds back certain deductions and preference items that are allowed under the regular tax system. This wider base, combined with a flat-rate tax, ensures that taxpayers with large deductions still pay a meaningful federal tax bill.

Feature	Regular Tax System	AMT System
Tax base	Taxable income (AGI minus deductions)	AMTI — broader base, fewer deductions
Rates	Graduated: 10% to 37%	Flat: 26% on first $232,600 of AMTI; 28% above
Standard deduction	Allowed ($15,000 single / $30,000 MFJ in 2025)	Replaced by AMT exemption ($88,100 single / $137,000 MFJ in 2025)
State/local tax deduction	Allowed (capped at $10,000)	Not allowed
Personal exemptions	Suspended under TCJA	N/A

Tip: You do not owe additional AMT if your regular tax exceeds your tentative minimum tax (TMT). The AMT only applies when the TMT is higher than your regular tax after credits.

Alternative Minimum Taxable Income (AMTI) starts with your regular taxable income and then adds back specific preference items and adjustments. The result is reduced by the AMT exemption, and the remaining amount is taxed at the AMT rates.

• Start with: Regular taxable income
• Add back: State and local tax deductions, miscellaneous itemized deductions, standard deduction (if taken), certain depreciation adjustments, ISO exercise spreads, and tax-exempt interest from private activity bonds
• Equals: AMTI
• Subtract: AMT exemption (phased out at higher income)
• Equals: AMT base
• Multiply by: 26% (first $232,600) / 28% (above $232,600)
• Equals: Tentative Minimum Tax (TMT)
• You pay: Max(regular tax, TMT)

AMT Item	2025 Amount
AMT exemption — Single	$88,100
AMT exemption — Married Filing Jointly	$137,000
Exemption phase-out begins — Single	$626,350 AMTI
Exemption phase-out begins — MFJ	$1,252,700 AMTI
AMT rate — first $232,600 of AMTI above exemption	26%
AMT rate — above $232,600	28%

Tip: Use IRS Form 6251 (Alternative Minimum Tax — Individuals) to calculate your AMT liability. Many tax software packages run this calculation automatically and notify you if AMT applies.

The Tax Cuts and Jobs Act of 2017 dramatically raised AMT exemptions and phase-out thresholds, effectively removing most middle-income taxpayers from AMT exposure. As of 2025, the AMT primarily affects a narrower set of high-income situations.

Common AMT Trigger	Why It Creates AMT Exposure
Exercising incentive stock options (ISOs)	The spread (FMV minus exercise price) is added to AMTI in the year of exercise, even though regular tax is not triggered until the shares are sold
Large state income tax or property tax deductions	SALT deduction is fully disallowed under AMT (regular tax caps it at $10,000; AMT allows $0)
High income in a high-tax state	Combination of large state tax deduction add-back and high overall income pushes AMTI above the exemption
Private activity bond interest	Tax-exempt for regular purposes but counted in AMTI
Accelerated depreciation (business assets)	AMT requires slower depreciation schedules than regular tax for some assets
Large miscellaneous itemized deductions	No longer applicable post-TCJA (most miscellaneous deductions suspended); watch for future law changes

The most dangerous single-year AMT event for employees is a large ISO exercise at a low strike price. A tech employee exercising $2 million of ISOs with a $10 strike on stock trading at $110 creates a $2 million AMTI addition — potentially triggering $500,000+ in AMT even though no stock was sold.

Warning: Paying AMT in the year you exercise ISOs does not eliminate tax on the stock — it is a prepayment. If the stock later drops below your exercise price, you may have paid AMT on phantom income you never actually received in cash.

The AMT achieves its broader tax base primarily by disallowing or modifying deductions that are valid under the regular tax system. Understanding which deductions are at risk is essential for planning.

Deduction	Regular Tax Treatment	AMT Treatment
State and local taxes (SALT)	Deductible up to $10,000 (itemized)	Fully disallowed — added back to AMTI
Standard deduction	$15,000 single / $30,000 MFJ (2025)	Not allowed (replaced by AMT exemption)
Home equity loan interest (non-acquisition)	Deductible on Schedule A	Not deductible under AMT
Percentage depletion in excess of cost	Deductible for oil/gas, mining	Preference item; added back to AMTI
Accelerated MACRS depreciation (some assets)	Allowed under regular tax	Must use AMT depreciation schedule (slower)
Charitable contributions	Deductible	Allowed under AMT
Mortgage interest (acquisition debt)	Deductible on Schedule A	Allowed under AMT

Notably, medical expenses and charitable deductions are allowed under AMT with the same or similar rules as regular tax. The biggest AMT culprit for most high earners — SALT — is fully disallowed, which explains why residents of California, New York, and New Jersey (with high state taxes) are disproportionately exposed.

Tip: If you are subject to AMT, itemizing deductions may provide less benefit than expected because large itemized deductions (especially SALT) are added back in the AMT calculation. Run both scenarios before deciding whether to itemize or take the standard deduction.

AMT planning is a year-round exercise, not a last-minute April filing decision. The following strategies can reduce or eliminate AMT exposure for affected taxpayers.

• ISO exercise timing: Exercise ISOs in a year when other AMTI additions are low, or exercise only as many options as can be absorbed without triggering AMT. Use an ISO modeling tool to calculate the AMT crossover point before exercising.
• Spread ISO exercises across tax years: Exercising some options each year keeps the ISO spread small enough to stay under the AMT threshold.
• Use AMT credit in future years: AMT paid due to ISO exercises generates an AMT credit (Form 8801) that can be used to reduce regular tax in future years when you are not subject to AMT — particularly valuable when the stock is held and eventually sold.
• Defer state tax payments: Do not prepay state estimated taxes in December if you are subject to AMT — the deduction is worthless under AMT, and prepayment converts a potential regular-tax deduction into zero benefit.
• Accelerate income: In some cases, recognizing more ordinary income in a high-AMTI year can paradoxically reduce AMT by increasing regular tax above the tentative minimum tax.

Strategy	Best For	Potential Savings
ISO exercise planning / modeling	Employees with stock options	Can avoid six-figure AMT bills
Claiming AMT credit carryforward	Anyone who paid prior-year AMT	Dollar-for-dollar reduction in future regular tax
Avoid December state tax prepayment	High-tax state residents	Modest; avoids wasting a deduction
Qualified Small Business Stock (QSBS)	Angel investors / startup employees	QSBS gain exclusion applies under AMT as well as regular tax

Tip: The AMT credit carryforward is often overlooked. If you paid AMT in a prior year due to ISO exercises, that credit can offset regular tax in future years — track it carefully on Form 8801 and do not let it go unused.