Insight vol 2:
Time of Birth, Length of Ministry. Jesus evidently was born in the month of Ethanim (September-October) of the year 2 B.C.E., was baptized about the same time of the year in 29 C.E., and died about 3:00 p.m. on Friday, the 14th day of the spring month of Nisan (March-April), 33 C.E. The basis for these dates is as follows:
Jesus was born approximately six months after the birth of his relative John (the Baptizer), during the rule of Roman Emperor Caesar Augustus (31 B.C.E.–14 C.E.) and the Syrian governorship of Quirinius (see REGISTRATION for the probable dates of Quirinius’ administration), and toward the close of the reign of Herod the Great over Judea.—Mt 2:1, 13, 20-22; Lu 1:24-31, 36; 2:1, 2, 7.
His birth in relation to Herod’s death. While the date of Herod’s death is a debated one, there is considerable evidence pointing to 1 B.C.E. (See HEROD No. 1 [Date of His Death]; CHRONOLOGY [Lunar eclipses].) A number of events intervened between the time of Jesus’ birth and Herod’s death. These included Jesus’ circumcision on the eighth day (Lu 2:21); his being brought to the temple in Jerusalem 40 days after birth (Lu 2:22, 23; Le 12:1-4, 8); the journey of the astrologers “from eastern parts” to Bethlehem (where Jesus was no longer in a manger but in a house—Mt 2:1-11; compare Lu 2:7, 15, 16); Joseph and Mary’s flight to Egypt with the young child (Mt 2:13-15); followed by Herod’s realization that the astrologers had not followed his instructions, and the subsequent slaughter of all boys in Bethlehem and its districts under the age of two years (indicating that Jesus was not then a newborn infant). (Mt 2:16-18) Jesus’ birth taking place in the fall of 2 B.C.E. would allow for the time required by these events intervening between his birth and the death of Herod, likely in 1 B.C.E. There is, however, added reason for placing Jesus’ birth in 2 B.C.E.
Relationship to John’s ministry. Further basis for the dates given at the start of this section is found at Luke 3:1-3, which shows that John the Baptizer began his preaching and baptizing in “the fifteenth year of the reign of Tiberius Caesar.” That 15th year ran from the latter half of 28 C.E. to August or September of 29 C.E. (See TIBERIUS.) At some point in John’s ministry, Jesus went to him and was baptized. When Jesus thereafter commenced his own ministry he was “about thirty years old.” (Lu 3:21-23) At the age of 30, the age at which David became king, Jesus would no longer be subject to human parents.—2Sa 5:4, 5; compare Lu 2:51.
According to Numbers 4:1-3, 22, 23, 29, 30, those going into sanctuary service under the Law covenant were “from thirty years old upward.” It is reasonable that John the Baptizer, who was a Levite and son of a priest, began his ministry at the same age, not at the temple, of course, but in the special assignment Jehovah had outlined for him. (Lu 1:1-17, 67, 76-79) The specific mention (twice) of the age difference between John and Jesus and the correlation between the appearances and messages of Jehovah’s angel in announcing the births of the two sons (Lu 1) give ample basis for believing that their ministries followed a similar timetable, that is, the start of John’s ministry (as the forerunner of Jesus) being followed about six months later by the commencement of Jesus’ ministry.
On this basis, John’s birth occurred 30 years before he began his ministry in Tiberius’ 15th year, hence somewhere between the latter half of 3 B.C.E. and August or September of 2 B.C.E., with Jesus’ birth following about six months later.