You may have noticed historians or archaeologists using abbreviations like B.C.E. to discuss something that happened thousands of years ago. But what is the difference between A.D. and C.E., or B.C. and B.C.E.? Do they mean the same thing, and, if so, which do archaeologists tend to use?

The widely used Gregorian calendar is based on the estimated birth date of Jesus Christ. Subsequent years count up from this event and are accompanied by either A.D. or C.E., while the preceding years count down from it and are accompanied by either B.C. or B.C.E. The date 2,000 B.C. means 2,000 years before the birth of Jesus. In 2020, that date would have been 4,020 years ago! This is the way many people in Europe and the Americas have traditionally kept track of years.

Archaeologists often decide to annotate dates using B.C.E. (before common era) and C.E. (common era) rather than B.C. (before Christ) and A.D. (Anno Domini). B.C.E. and C.E. dates are essentially identical to B.C. and A.D., however, many archaeologists feel that the former are preferable for two reasons: first, B.C. and A.D. suggest a eurocentric world view that is not necessarily appropriate when discussing cultures that existed in North America almost 10,000 years prior to European contact; second, there is some confusion over the actual birth date of Jesus, with most experts placing the birth between 7 and 4 years before the year 1. The designations B.C.E. and C.E. don’t rely on any particular event in history, instead, they consider the year 1 to simply be the year that has traditionally been designated as 1.

The use of B.P. (before present) is also fairly standard in the dating of prehistoric events that span a significant length of time. This annotation can be confusing when referencing more recent dates because the present changes every year (B.P. has to be constantly updated) and referring to the year 1865 as 156 B.P. would probably not help to explain events related to historic period archaeology. 

What do different date abbreviations mean?

A.D. (Anno Domini, year of the Lord) and B.C. (before Christ) have long been used by scholars in Europe and the Americas; their reference point is the birth of Christ.

C.E. (current era) and B.C.E. (before current era) are sometimes used instead of A.D. and B.C. as a way to express a date without specifically referencing a Eurocentric worldview. But the dates themselves are the same as dates expressed as A.D. or B.C. For example, 1865 C.E. is the same year as A.D. 1865, and 2000 B.C.E. is the same year as 2000 B.C.

B.P. (before the present) is the number of years before the present.