In the tenth year of Ahaz king of Judah began Hoshea the son of Elah to reign in Samaria over Israel nine years. In this account there is some difficulty, since it was in the twentieth of Jotham, that is, the fourth of Ahaz, that Hosea conspired against Pekah king of Israel, and slew him, when it might be reasonably thought he began his reign: now either there was an interregnum until the twelfth of Ahaz, or Hoshea however was not generally received and acknowledged as king till then, as others think; he being a tributary to the king of Assyria, and a kind of viceroy, is not said to reign until he rebelled against him; after which he reigned nine years, four in the times of Ahaz, and five in the reign of Hezekiah, 2 Kings 18:9, in this way the author of the Jewish chronology goes r, in which he is followed by other Jewish writers; and this bids as fair as any to remove the difficulty, unless these nine years refer to the time of his reign before the twelfth of Ahaz; and the sense be, that in the twelfth of Ahaz he had reigned nine year's; but it is said he "began" to reign then.
r Seder Olam Rabba, c. 22.