Hoshea began to rule over Israel in 732 BC.
Hosea's reign is noted as starting in the twentieth year of Jotham (2 Kings 15:30) and during the twelfth year of King Ahaz's rule in Judah. Ahaz likely co-ruled with Jotham from around 743 BC, when he was twelve, but his official reign started in 731 BC (2 Kings 16:2). Therefore, the references to Ahaz's reign align.