What is the difference between 1 BC and 1 AD?In the AD year numbering system, whether applied to the Julian or Gregorian calendars, AD 1 is preceded by 1 BC. There is no year "0" between them, so a new century begins in a year which has "01" as the final digits (e.g., 1801, 1901, 2001). New millennia likewise are considered to have begun in 1001 and 2001.
en.wikipedia.org/wiki/Anno_Domini