Source: U.S. Department of the Treasury. Internal Revenue Service  

Release: SOI Tax Stats - Historical Data Tables  

Units:  Number of Returns, Not Seasonally Adjusted

Frequency:  Annual

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.