In the fifteenth year of the reign of Tiberius Caesar, Pontius Pilate being governor of Judea, and Herod being tetrarch of Galilee, and his brother Philip tetrarch of the region of Ituraea and Trachonitis, and Lysanias tetrarch of Abilene, during the high priesthood of Annas and Caiaphas, the word of God came to John the son of Zechariah in the wilderness. (Luke 3:1-2)We have several persons occupying various offices mentioned here that can specify this date: Tiberius Caesar, Pontius Pilate, Herod, Philip, Lysanias, high priesthood of Annas and Caiaphas. They ruled as follows.
|Tiberius Caesar||Emperor||Rome||(12 or) 14 AD||37 AD|
|Pontius Pilate||Governor||Judea||26 AD||36 AD|
|Herod||Tetrarch||Galilee||1 BC||37 AD|
|Philip||Tetrarch||Ituraea and Trachonitis||1 BC||34 AD|
|Caiaphas||High priest||Israel||18 AD||36 AD|
Annas was deposed as high priest in 15 AD but continued to have some influence.
The dates above confine the beginning of John the Baptist's ministry to between 26 and 34 AD. Tiberius became the emperor in 14 AD. He may have been co-emperor with Augustus from 12 AD. Depending on whether his reign is considered as starting from 12 or 14 AD and depending on whether Luke was using ascension or non-ascension reckoning, John the Baptist's ministry began between 26 and 29 AD.
If Jesus started his ministry when he was about 30 (or about to turn 30) and he was born between 3 and 1 BC then the dates narrow to 27 to 29 AD.