Different tax rate structures for the regular income tax applied to Tax Years 1999-2013. Indexing of tax rate boundaries for inflation existed. The preferential maximum tax rate on net long-term capital gains under "alternative tax" was revised over the years. Alternative tax was abolished, but a maximum capital gain tax rate less than the maximum regular tax rate continued to apply under certain conditions.
Includes "alternative minimum tax" (AMT), starting with 2000. For previous years, AMT was excluded and was reflected only in "total income tax".
For additional information about the return filing requirements, see the annual reports, Statistics of Income-Individual Income Tax Returns at https://www.irs.gov/uac/soi-tax-stats-historical-data-tables.
U.S. Department of the Treasury. Internal Revenue Service, Individual Income Tax Filing: Income Tax Before Credits [INCTXBCTA], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/INCTXBCTA, May 23, 2019.