When did Ahaziah begin his reign?

Answer:

"Ahaziah was twenty-two years old when he became king, and he reigned one year in Jerusalem. His mother's name was Athaliah the granddaughter of Omri, king of Israel" (II Kings 8:26).

"Ahaziah was forty-two years old when he became king, and he reigned one year in Jerusalem. His mother's name was Athaliah the granddaughter of Omri" (II Chronicles 22:2).

This is a case where it appears a scribe made a mistake in copying II Chronicles 22:2. Scholars are confident of this because II Chronicles 21:20 and II Kings 8:17 tells us that Ahaziah's father died at the age of 40. If Ahaziah was 42 at the time of his father's death, he would have been two years older than his father -- an impossibility. In older Hebrew, numbers were represented by single letters. The letter for forty was mem and the letter for twenty was kaph. It is possible that these two similar letters in ancient Hebrew were confused in the ancient Hebrew manuscripts. When the letters were expanded to words, the error was carried over. This is further supported in that some Septuagint translations of the Hebrew Bible, the Arabic manuscript, and the Syriac manuscript have twenty-two in II Chronicles 22:2 instead of forty-two as found in the Masoretic family of manuscripts.

Some try to make both texts "right" by asserting that Ahaziah did not immediately start his reign, but was under the thumb of his regent mother. This doesn't work as we look at the reign of Jehoram, Ahaziah's uncle. In II Kings 3:1 we learn that Jehoram ruled twelve years, starting at the eighteenth year of Jehoshaphat's reign in Israel. During Jehoram of Israel's fifth year of reign, Jehoram of Judah began to reign (II Kings 8:16). Azahiah began his reign during Jehoram of Israel's final year and died with him at the hand of Jehu. There is no room to slip in an extra 20 years.