The statistics for all years shown are comparable. However, prior to Tax Year 2000, total income tax is the sum of two components, income tax after credits and "minimum tax" or "alternative minimum tax (AMT)". Starting with Tax Year 2000, total income tax is, in general, the same as income tax after credits, which was redefined to include AMT. (The small difference between the two amounts for 2000 is due mainly to the inclusion in the statistics for Tax Year 2000 of prior-year returns filed in Calendar Year 2001 that were used as proxies for Tax Year 2000 returns filed after 2001; the AMT on these returns was included in total income tax, but not in income tax before or after credits, consistent with the reporting sequence on the tax return forms for these years. The same is true for Tax Year 2002 for prior returns filed in Calendar Year 2003 for Tax Year 2000 and earlier. To a far lesser extent, the difference between total income tax and income tax after credits represents the tax on accumulation distributions of trusts, which was included in total income tax only.) Total income tax reflects the amount reported on the tax return and is, therefore, before any examination or enforcement activities by the Internal Revenue Service. It represents the income tax liability that was payable to the U.S. Department of the Treasury.
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: Total Income Tax [TLINCTX], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/TLINCTX, February 26, 2021.