Alternative minimum tax (AMT) is a supplemental income tax that applies to certain individuals in some situations. This type of tax does not come up for many taxpayers, but higher income earners and people in special situations may have to pay large AMT bills. AMT was first enacted in 1979 in response to reports that 155 wealthy individuals had paid no income tax in 1966. It is not the same as ordinary income tax or employment tax, and is calculated according to its own rules.