We cannot say with absolute certainty the year Jesus was baptized, but using biblical data we can give a date with an uncertainty of one year or, at most two or three years.
To establish the date of the baptism of Jesus, one must first establish the date of his death. The traditional date of AD 33 is almost certainly not correct. It is based on the assumption that Jesus was born in 0AD, that his ministry started when he was 30 and ended three years later. The first two assumptions are almost certainly not ture. First of all, there was no year zero. Second, the Bible does NOT say that Jesus was exactly thirty when he began his ministry. What we can say is that he was most likely at least thirty when he began his ministry. From biblical evidence, especially the fact that Herod (who murdered the male children in Bethlehem) died in 4 BC, we can conclude that Jesus was most likely born in 5 or 6 BC. From evidence about the timing of the Passover, Jesus died in a year when the eve of the Passover, the Seder meal, occurred on a Thursday evening, which included Friday until sundown. This makes the year Jesus died most likely AD 30 or possibly AD 29. If we assume that the ministry of Jesus lasted the tradional three years, then Jesus was baptized in AD 26 or 27. Some believe that the ministry of Jesus lasted less than three years. Very few scholars believe it lasted more than three years. In fact, I do not know of any good scholars who say this. If we allow that the ministry of Jesus was less than three years, then perhaps he was baptized in the year AD 28. The date of his baptism is not a huge issue as far as I know to any important biblical teaching, but we can say with confidence that Jesus was baptized somewhere between AD 26-28.