From TheBalance.com….
The Alternative Minimum Tax is a mandatory alternative to the standard income tax. It gets triggered when taxpayers make more than the exemption and use many common itemized deductions. The exemption is $113,400 for joint filers and $72,900 for individuals.1
The reason the AMT catches those in higher tax brackets is that it eliminates many of those deductions. The AMT hits 60% of the taxpayers making between $200,000 and $500,000.2