Some people translate anno Domini as "in the year of our Lord", but there is no Latin noster, "our", in the phrase. A.D. is written before the year, usually with small capital letters, with no separating comma, as: A.D. 1995; or informally, after the year, as: about 1450 A.D. Anno Domini is supposed to indicate the number of years from the birth of Chirst.

In the sixth century, Dionysius Exiguus initiated the system of expressing dates by referring events to the birth of Christ. According to his calculations, Christ was born in 754 A.U.C. (abbreviation, ab urbe condita; from [since] the founding of the city [Rome], c. 753 B.C.); however, it is generally agreed that Christ was born at least four years before the date that was set by Dionysius.