Taxation in the US: Alternative minimum tax: Part 1

The alternative minimum tax (AMT) is a tax imposed by the United States federal government in addition to the regular income tax for certain individuals, estates, and trusts. As of tax year 2018, the AMT raises about $5.2 billion, or 0.4% of all federal income tax revenue, affecting 0.1% of taxpayers, mostly in the upper income ranges.

An alternative minimum taxable income (AMTI) is calculated, by taking the ordinary income and adding disallowed items and credits such as state and local tax deductions, interest on private-activity municipal bonds, the bargain element of incentive stock options, foreign tax credits, and home equity loan interest deductions. This broadens the base of taxable items. Many deductions, such as mortgage home loan interest and charitable deductions, are still allowed under AMT. The AMT is then imposed on this AMTI at a rate of 26% or 28%, with a much higher exemption than the regular income tax.

The Tax Cuts and Jobs Act of 2017 (TCJA) reduced the fraction of taxpayers who owed the AMT from 3% in 2017 to 0.1% in 2018, including from 27% to 0.4% of those earning $200,000 to $500,000, from 61.9% to 2% of those earning $500,000 and $1,000,000.

The major reasons for the reduction of AMT taxpayers after TCJA include the capping of the state and local tax deduction (SALT) by the TCJA at $10,000, and a large increase in the exemption amount and phaseout threshold. A married couple earning $200,000 now requires over $50,000 of AMT adjustments to begin paying the AMT. The AMT previously applied in 2017 and earlier to many taxpayers earning from $200,000 to $500,000 because state and local taxes were fully deductible under the regular tax code but not at all under AMT. Despite the cap of the SALT deduction, the vast majority of AMT taxpayers paid less under the 2018 rules.

The AMT was originally designed to tax high-income taxpayers who used the regular tax system to pay little or no tax. Due to inflation and cuts in ordinary tax rates, many middle-income taxpayers began to pay the AMT. The number of households owing AMT rose from 200,000 in 1982 to 5.2 million in 2017, but was reduced back to 200,000 in 2018 by the TCJA. After the expiry of the TCJA in 2025, the number of AMT taxpayers is expected to rise to 7 million in 2026.