How Alternative Minimum Tax (AMT) Calculator Works
The AMT Calculator helps taxpayers determine whether they owe Alternative Minimum Tax by computing their tax liability under both the regular tax system and the AMT system, then identifying which produces the higher amount. The AMT was designed to ensure high-income taxpayers cannot use deductions and preferences to avoid paying a minimum level of tax.
The tool starts with your regular taxable income and adds back AMT preference items — deductions and exclusions allowed under the regular tax code but disallowed under AMT. Common adjustments include state and local tax (SALT) deductions, miscellaneous itemized deductions, private activity bond interest, and the difference between ISO exercise price and fair market value for incentive stock options.
After computing your Alternative Minimum Taxable Income (AMTI), the tool subtracts the AMT exemption amount (which phases out at higher income levels) and applies the AMT tax rates: 26% on the first portion and 28% on amounts above the threshold. If your tentative minimum tax exceeds your regular tax liability, you owe AMT equal to the difference.
The calculator is particularly valuable for employees exercising incentive stock options (ISOs), as the bargain element at exercise is an AMT preference item that can create substantial unexpected tax liability. It also helps high-income taxpayers in high-tax states understand SALT deduction limitations under AMT. Use it alongside the Cost Segregation Study Estimator to understand how real estate depreciation interacts with AMT for high-income investors.
Key Terms Explained
- Alternative Minimum Tax (AMT)
- A parallel tax system that limits the benefit of certain deductions and credits to ensure a minimum level of tax is paid.
- AMT Preference Items
- Deductions and income exclusions that are added back to regular taxable income when computing AMTI.
- AMTI (Alternative Minimum Taxable Income)
- The tax base used for AMT calculations, computed by adjusting regular taxable income for AMT preferences.
- AMT Exemption
- A fixed dollar amount subtracted from AMTI before applying AMT rates, which phases out at higher income levels.
- AMT Credit Carryforward
- A credit for AMT paid in prior years due to timing differences (like ISOs) that can offset regular tax in future years.
- Incentive Stock Options (ISOs)
- Employee stock options with favorable regular tax treatment but that create AMT preference items when exercised.
Who Needs This Tool
Calculating how many ISOs to exercise in a single year without triggering AMT, optimizing the exercise strategy across multiple tax years.
Determining whether large state income tax and property tax deductions will trigger AMT liability.
Running multiple scenarios for a client to find the optimal combination of deductions and ISO exercises that minimizes total tax across regular and AMT systems.
Evaluating whether accelerated depreciation from a cost segregation study will create AMT exposure.
Methodology & Formulas
AMTI = Regular Taxable Income + AMT Preference Items + AMT Adjustments. AMT Exemption phases out at 25 cents per dollar above threshold (exemption amounts and thresholds indexed annually). Tentative Minimum Tax = 26% × first $232,600 of (AMTI - Exemption) + 28% × excess. AMT Owed = max(0, Tentative Minimum Tax - Regular Tax Liability). For ISOs: AMT Adjustment = (FMV at Exercise - Exercise Price) × Number of Shares.
Pro Tips
- If you exercise ISOs, model different quantities and timing — spreading exercises across tax years can keep you below AMT thresholds each year.
- AMT paid on timing items like ISO exercises generates an AMT credit carryforward that reduces your regular tax in future years.
- The SALT cap ($10,000) under regular tax actually reduces AMT exposure since you can no longer deduct large state taxes that would be added back for AMT.
- Long-term capital gains and qualified dividends are taxed at the same preferential rates under both regular and AMT systems — they rarely trigger AMT on their own.
- Run the calculation before year-end so you can make adjustments like deferring ISO exercises or accelerating income to optimize your overall position.