What it means
The AMT was introduced in 1969 after Congress learned that a number of very high earners had paid no federal income tax by combining legitimate deductions and exclusions. Rather than remove the deductions, Congress created a second tax system that limits them.
Every year, a taxpayer's return effectively runs twice: once under the regular rules and once under the AMT rules, which disallow or reduce many of the items that lower regular tax. If the AMT calculation produces a higher liability, the taxpayer pays the difference as AMT on top of the regular tax.
The items most likely to trigger AMT for individuals are the exercise of incentive stock options (the spread between exercise price and market value is income for AMT even though it is not for regular tax until the shares are sold), interest on certain private activity municipal bonds, and large state and local tax deductions, though the latter matters less since the regular deduction was capped. Because the AMT exemption is large and phases out only at high incomes, most middle-income taxpayers are no longer affected, and the corporate AMT was repealed in 2017 and replaced in 2023 by a different minimum tax on the book income of very large corporations.
AMT paid because of timing differences, such as option exercises, generates a credit that can be used against regular tax in future years when regular tax exceeds AMT. That credit prevents double taxation over time but can take years to recover, and taxpayers who exercise options and then see the shares fall in value can find themselves paying AMT on gains that never materialised.
That trap, and its planning implications, is why AMT remains important for anyone with equity compensation. The AMT is a United States concept, though other countries have minimum tax rules with similar aims.
Its details, exemptions and thresholds are adjusted for inflation and changed by legislation, so the specific figures in any given year should be checked against current guidance.
In practice
Real-world examples.
Example
A start-up employee exercises incentive stock options worth $400,000 in spread and is surprised by a $90,000 AMT bill in a year when she received no cash from the shares.
Example
A retiree holding private activity municipal bonds finds that the interest, tax-exempt for regular purposes, is added back for AMT and pushes him into paying the minimum tax.
Example
A high-earning couple in a high-tax state check each year whether the AMT applies, and find that since the cap on state and local tax deductions it no longer does.
Think of it
“AMT is a backup tax system that catches taxpayers who use lots of deductions-ensuring everyone pays something.
Formula
Calculation
Alternative Minimum Taxable Income (AMTI) = Regular Taxable Income + AMT Adjustments and Preference Items
AMT Base = AMTI minus AMT Exemption (the exemption phases out above an income threshold)
Tentative Minimum Tax = 26% x AMT Base up to the rate threshold + 28% x the excess
AMT Payable = Tentative Minimum Tax minus Regular Tax, if positive
Worked example (illustrative figures; the actual exemption, thresholds and rate bands are indexed and should be checked for the tax year). A software engineer has regular taxable income of $180,000 and regular tax of $33,000. During the year she exercised incentive stock options on 10,000 shares at $5 when the market price was $35, creating a spread of $300,000 that is an AMT adjustment but not regular income. Assume an AMT exemption of $85,000 that begins to phase out at $600,000 of AMTI, and a 26% rate on the first $220,000 of the AMT base with 28% above.
- AMTI = $180,000 + $300,000 = $480,000
- AMT exemption = $85,000 (no phase-out, since AMTI is below the threshold)
- AMT base = $480,000 minus $85,000 = $395,000
- Tentative minimum tax = 26% x $220,000 + 28% x $175,000 = $57,200 + $49,000 = $106,200
- AMT payable = $106,200 minus $33,000 = $73,200
Her total federal tax is $106,200 rather than $33,000, on shares she has not sold. The $73,200 becomes an AMT credit that she can use in future years when her regular tax exceeds her tentative minimum tax, but if the shares fall to $10 before she sells, she will have paid tax on $300,000 of paper gain and realised only $50,000. Planning options include exercising fewer options per year to stay under the AMT crossover, exercising early in the year so that a fall in price can be dealt with by selling before year end, or selling in the same year as exercise to convert the transaction into regular income.Case study
Seen in the real world.
An engineer at a technology company exercised all 40,000 of his incentive stock options in November at $2 when the shares traded at $40, on the advice of a colleague that holding for a year would qualify the gain for long-term capital gains rates. The spread of $1.52 million was AMT income. His tax adviser, consulted in February, calculated an AMT liability of about $400,000, due in April.
The share price had fallen to $18 by then, making the shares worth $720,000, and a lock-up prevented him selling most of them. He borrowed against the shares to pay the tax, the price fell further, and he ended the following year with an AMT credit he would take a decade to use and shares worth less than the tax he had paid on them.
Had he exercised in January instead of November, he could have sold the shares before year end when the price fell, converting the exercise into a regular-tax event on the actual gain. His adviser's rule for every client with options thereafter was: model the AMT before exercising, exercise early in the year, and never let the tax on a paper gain exceed what the shares could be sold for.
Watch out
Common mistakes.
- Exercising incentive stock options late in the year without modelling the AMT. The tax is due on the spread whether or not the shares can be sold.
- Assuming the AMT no longer exists. The individual AMT affects fewer people than before but remains fully in force for those with the triggering items.
- Forgetting the AMT credit. AMT paid on timing items can be recovered in later years, and the credit must be tracked and claimed.
Questions
People also ask.
Who pays the alternative minimum tax?
Mainly taxpayers with large incentive stock option exercises, certain tax-exempt interest, or combinations of deductions that the AMT rules disallow, and with income above the exemption phase-out.
What is the AMT credit?
The AMT paid on timing differences becomes a credit against regular tax in future years when regular tax exceeds tentative minimum tax, so the same income is not taxed twice over time.
Does the AMT apply to companies?
The original corporate AMT was repealed for tax years after 2017. A separate corporate minimum tax on the financial statement income of very large corporations applies from 2023.
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