Albert Barnes Commentary 1 Kings 16:29

"And in the thirty and eighth year of Asa king of Judah began Ahab the son of Omri to reign over Israel: and Ahab the son of Omri reigned over Israel in Samaria twenty and two years." — 1 Kings 16:29 (ASV)

Twenty-two years - Rather, from a comparison between 1 Kings 15:10 and 1 Kings 22:51, it was not more than 21 years. Perhaps his reign did not much exceed 20 years.