The first day of the 20th century was January 1, 1901. The common calendar-century count starts with year 1, so the 20th century runs from 1901 through 2000.

Quick Scoop

  • First day: January 1, 1901.
  • Last day: December 31, 2000.
  • A lot of people assumed it began on January 1, 1900, but that would only happen if year 0 existed in the numbering system; it does not in the Gregorian/Common Era count.

If you want, I can also explain why the “1900 vs. 1901” century debate happens in one simple example.