What was the length of Jesus' public ministry?

The Bible does not tell us the exact number of days Jesus Christ served in public ministry. However, a close look at the chronological data revealed in the Gospels allows us to carefully reconstruct a timeline with a good degree of accuracy.
To begin, Luke noted that the ministry of John the Baptist began in the 15th year of Tiberius Caesar's reign, which was the year AD 26. Jesus began to minister shortly after this time at approximately the age of 30 (or perhaps "early 30s"; Luke 3:23). His crucifixion took place in either AD 30 or 33, indicating that His public ministry took place within the AD 26—33 timeframe.

More specifically, scholars note that if Jesus began His public ministry between mid to late AD 26 and died in the spring of AD 30, His ministry would have been a total of 3½ years (including His resurrection, 40 days of appearances, and ascension). Others who argue for the crucifixion taking place in AD 33 argue that Jesus did not begin His ministry until AD 29, calculating the starting date of Tiberius Caesar's reign based upon the death of his predecessor Augustus Caesar in AD 14, meaning that the ministry of John the Baptist began in AD 29. In either case, a public ministry of about 3½ years is still the conclusion.

Further evidence for this length of time can also be found in the Jewish festivals. In John's Gospel, Jesus attended at least three annual Passover feasts (John 2:13; 6:4; 11:55-57). At the shortest, His ministry would have been 2½ years. If one additional Passover occurred during this time, sometime between John 2 and 6, the information regarding 3½ years fits nicely.

In fact, this unmentioned Passover likely took place prior to the three occasions mentioned in John. By the time of the first Passover mentioned in John 2:13, Jesus had already been baptized, spent 40 days being tempted in the wilderness, had started preaching in various towns and villages (Matthew 4:17), selected His first followers (John 1:35-51), performed His first miracle at Cana in Galilee (John 2:1-11), and traveled to Capernaum north of the Sea of Galilee (John 2:12). These efforts would have covered the course of several months, adding enough time to easily fit the 3½ years mentioned above.

Based on this information, the public ministry of Jesus holds profound implications. In only about 1,200 days, Jesus gathered a small group of followers, taught crowds in a variety of towns, performed miracles, healed diseased, cast out evil spirits, and became such a "threat" to the Jewish religious leaders that they sought to put Him to death. After His resurrection, Jesus appeared to many people over 40 days, preparing His followers to continue His mission to take the good news to "all nations" (Matthew 28:18-20) until His return.