דברי הימים ב, פרק כ״ז, פסוק ז׳

The historical records of Jotham are documented in the Book of the Kings of Israel and Judah. When reviewing these accounts, a distinct difference emerges in how the two kingdoms counted the years of his rule. The kings of Israel included the period when Jotham served as a judge over the people, even though his father was still alive at the time. They factored this early period of shared leadership into the total count of his reign.

In contrast, a more specific approach is used to define his actual time as king. The double recording of both the years of Jotham's life and the years of his reign serves a clear purpose. It specifically highlights and counts only the time he ruled actively and independently after his father passed away [מלבי״ם].