Since the late 1500’s our calendars have been divided into two great epochs: A.D. which stands for anno domini or “year of the Lord,” and B.C. which stands for “before Christ.” Clearly, those who created our calendar intended to divide history into two parts, with the birth of Christ marking the change from one era to the next. Unfortunately, they were off by a few years, which means that we cannot say that Jesus was born in the year A.D. 1. The question is, then, in what year was Christ born?

The key to discovering the date for any event in ancient history is to determine the latest possible date and the earliest possible date for it to have occurred, based upon more well-established dates for other events. So, Luke 2:1 tells us that Jesus was born during the reign of the Roman Emperor Augustus. Augustus ruled from 44 B.C. to A.D. 14. Based upon this information alone we can limit Christ’s birth to somewhere between these years. We can, however, narrow that range considerably when we look at other information provided by the Gospel writers.

While we know that Caesar was the Roman Emperor when Christ was born, we are also told in Matthew’s and Luke’s Gospels that Herod the Great was the appointed ruler of Judea when Jesus was born (see Matthew 2:1, 7, 16, 19 and Luke 1:5). Herod was proclaimed king of the Jews by the Roman Senate in 40 B.C. and ruled until his death in the Spring of 4 B.C. Therefore, the latest possible date for Christ’s birth would have been early in the year 4 B.C.

Determining the earliest possible date for Christ’s birth is much more difficult. Luke mentions the taking of a census at that time, but scholars have had great difficulty determining exactly which census Luke has in mind or when it occurred. More helpful is Luke’s statement that John the Baptist began his ministry of baptism in the wilderness in the fifteenth year of the reign of Tiberius (Luke 3:1). This would have most likely been in either A.D. 28 or 29. We will assume the earlier since we are trying to determine the earliest possible date for Christ’s birth.

Jesus’ ministry began in that same year, and later in the same chapter Luke tells us that Jesus was “about thirty years of age” when his ministry began. Obviously, the word “about” tells us that Jesus was not exactly thirty years old, but we should probably not add or subtract more than two or three years in order to stay within range of thirty. So, at most, Jesus was 33 when he began his ministry. He may have been twenty-nine or thirty-one, but since we are attempting to determine the earliest possible date for his birth we will use the highest end of the age-range. Now, if we assume that Jesus was thirty-three in the year A.D. 28, then the earliest possible year of his birth would be 6 B.C. (there is no year 0).

So, based upon these bits of evidence, we must conclude that Jesus was born in 6 or 5 B.C. or early 4 B.C. This is why the date of Christ’s birth is often claimed to be 6-4 B.C.