Why the AMT Exists
In 1969, Treasury Secretary Joseph Barr testified before Congress that 155 millionaires had paid zero federal income tax that year. They had done nothing illegal — they had simply stacked itemized deductions, claimed accelerated depreciation on investments, earned interest from tax-exempt bonds, and used other preferences that the regular tax code permitted. Public outrage was immediate and intense. Congress's response was the Alternative Minimum Tax: a parallel tax system designed to ensure that high-income taxpayers pay at least a minimum amount of federal tax regardless of how many deductions and preferences they claim.
The AMT does not replace the regular income tax. Instead, it runs alongside it. A taxpayer calculates their liability under both systems and pays whichever amount is greater. If your regular tax exceeds your AMT, you simply pay your regular tax and the AMT has no effect. If your AMT exceeds your regular tax, you pay the AMT — the difference between the two is reported separately on your return.
The underlying principle is straightforward: certain deductions and tax benefits are considered preferences that go beyond what is fair for the general population. The AMT systematically adds those preferences back into income before applying its own, flatter tax rates. It is designed to function as a floor beneath which no high-income taxpayer can fall through the use of aggressive deductions.
How AMT Is Calculated
AMT calculation starts with your regular taxable income and then makes a series of adjustments. Several items that are deductible under the regular tax system are disallowed under AMT. The standard deduction cannot be used. The SALT deduction — state and local taxes — is completely disallowed. The personal exemption, which was eliminated by TCJA but was significant historically, was also disallowed. These add-backs are called preference items.
One of the most significant AMT preference items for high earners today involves Incentive Stock Options (ISOs). When an employee exercises an ISO, the difference between the exercise price and the market price at the time of exercise — called the spread — is not treated as regular income and therefore generates no regular income tax at exercise. However, that spread is an AMT preference item. It gets added to AMT income even though it never appears in regular taxable income, which can produce a substantial AMT liability.
After adding preference items back to income, an AMT exemption is subtracted. For 2024, the exemption is $85,700 for single filers and $133,300 for married filing jointly. This exemption phases out at higher income levels. The resulting AMT income is taxed at 26% on the first $232,600 and 28% on amounts above that. These are lower headline rates than the top regular brackets, but the AMT income base is much broader because so many deductions have been stripped away.
Who Pays the AMT Today
Before TCJA took effect in 2018, approximately 5 million taxpayers paid the AMT each year. Many of these were upper-middle-income households — not the ultra-wealthy — in high-tax states like California, New York, and New Jersey, where large SALT deductions made them vulnerable to AMT exposure. They were paying relatively little in federal tax because their state and local tax deductions were so large, and the AMT was designed to prevent exactly that outcome.
TCJA changed the picture dramatically. It raised AMT exemptions and phase-out thresholds significantly, and it also capped SALT deductibility under the regular tax at $10,000 — meaning the regular tax system now disallows much of what the AMT had previously been catching. The combination pushed most former AMT payers back into the regular tax system. By 2024, fewer than 200,000 taxpayers pay the AMT.
However, the AMT remains critically relevant for one specific group: employees and executives who exercise Incentive Stock Options. The ISO spread can generate a large AMT liability with no corresponding cash in hand, particularly if the stock price declines after exercise but before the shares are sold. An employee might exercise a large ISO grant, trigger a substantial AMT bill, and then watch the stock fall — owing real taxes on paper gains that have already evaporated. This is one of the most serious tax planning pitfalls for startup and tech company employees.
Planning Around the AMT
For most taxpayers, AMT planning requires no action — they are simply not in AMT territory and the parallel system never affects them. For those who are, the primary lever is timing. In any year when you expect to be subject to AMT, generating additional preference items compounds your AMT liability without a corresponding increase in regular tax. The goal is to concentrate preference items into years when you are not subject to AMT.
ISO exercise timing is the most common AMT planning challenge. The key variables are the size of the spread, the current stock price and its trajectory, how early in the year the exercise occurs, and whether other income will push regular tax close to AMT levels in that year. Exercising a large ISO grant in a year when other income is low — or in a year when the regular tax rate and the AMT rate happen to be close — minimizes the after-tax cost of the AMT exposure.
The tax code also provides partial relief through the AMT credit. When you pay AMT in a given year, the amount by which your AMT exceeded your regular tax becomes a credit that you can carry forward and use in future years when your regular tax exceeds your AMT. This does not eliminate the cost of the AMT — you still lost the time value of money — but it means that AMT paid on ISO exercises is not necessarily a permanent extra cost. Careful multi-year planning, ideally with a tax advisor who understands equity compensation, is essential for anyone facing significant ISO decisions.