This is another Bible "fact" that isn't as cut-and-dried as you might think.

Nowhere in the New Testament does it explicitly say that Jesus' ministry — from his baptism by John until his crucifixion in Jerusalem — lasted three years. The way that number has been calculated is by counting how many times the Bible says that Jesus traveled to Jerusalem to celebrate Passover, the annual Jewish holiday commemorating the Exodus from Egypt.

In Mark, the earliest gospel, there's only one mention of a pilgrimage to Jerusalem, during which Jesus is arrested, tried and sentenced to death. By that calculation, some scholars think that Jesus' ministry was just one year or less.

But in the gospel of John, Jesus appears to make three separate pilgrimages to Jerusalem to observe Passover — John 2:13, John 6:4 and John 12:1 — and is killed during the third trip. That's where we get the idea that his ministry was three years long.

In fact, some experts place Jesus' death age at about 37 bearing in mind that he was born during King Herod's reign around 4 or 5 B.C.E., and that John the Baptist started preaching in the 15th year of Roman emperor Tiberius' reign (according to Luke 3:1), which would be 29 C.E. This is also when Jesus began his earthly ministry. Adding in three years for the three Passovers and these scholars determine that Jesus was 36 or 37 years old when he died.

But Bond says that John's repetition of the Jerusalem pilgrimage might reflect the author's theological interests more than any historical reality.

"The author of John is very keen on Jesus coming down to Jerusalem and being the replacement for Jewish feasts," says Bond, "so you have to ask, are there theological reasons for this or did Jesus' ministry really last that long?"

Another strike against the "three-year" theory is that the gospel of John, while important theologically, is "not generally noted for its historical accuracy," Bond says. John was the last of the gospel narratives of Jesus' life to be written, likely between 80 and 100 C.E., putting at least half a century between the author and the events he described.

Where does that leave us? Since it's unclear if Jesus' ministry was one year or three years long, and it's also unclear if Jesus was 30 or "about 30" when he began his ministry, it's very difficult to calculate with any certainty exactly how old Jesus was when he was crucified.