Anno Domini

Anno Domini (Medieval Latin : "in the year of the lord"), shortened as AD or A.D., is used to refer to the years after the birth of Jesus. AD is also a shortening for Christian Era.^[1] Similarly, Before Christ, shortened as BC or B.C., is used in the English language to refer to all years before the start of the time period Anno Domini. In past centuries, AD came before the year but comes after a century or millennium. For example, a person would write AD 2014 but 21st century AD or 3rd millennium AD. There is no zero year in this system. This means that the year A.D. 1 follows the year 1 B.C.

Some people mistakenly interpret “A.D.” as standing for “after death.” The abbreviation “A.D.” was originally placed before the year number (e.g. A.D. 145); then “B.C.” often placed after the year number (e.g. 145 B.C.). Nowadays it is more usual to put both abbreviations after the numbers (e.g. 145 AD; e.g. 145 BC).^[2]

This dating system was meant to signal the year of Christ's birth, but modern scholars have decided Jesus was actually born a few years earlier.

1. ↑ Abate, Oxford Pocket Dictionary and Thesaurus, s.v. "A.D."
2. ↑ "A.D. | Common Errors in English Usage and More | Washington State University".