OET interlinear 2 CHR 27:1

27:1 After a co-regency of eleven years with his father, Uzziah (750–740 BC), Jotham became king in his own right and reigned five more years (740–735 BC). This represents the sixteen years mentioned in the text. Jotham lived at least four more years, for we read that Hoshea came to power in the northern kingdom “in the twentieth year of Jotham son of Uzziah” (2 Kgs 15:30). But Jotham’s son, Ahaz, had already begun a co-regency with Jotham. After Jotham’s sixteen official years, Ahaz began to rule in his father’s stead (see study note on 2 Kgs 16:1-2). However, Ahaz presumably had his official accession ceremony following his father’s death in 732 BC, so the author of 2 Chronicles reckons Ahaz’s official regnal years starting in 731 BC (see 2 Chr 28:1).