מלכים א, פרק ט״ו, פסוק כ״ה

The transition of power in the Kingdom of Israel is carefully tracked alongside the timeline of the kings of Judah, creating a synchronized history of the two divided kingdoms. Nadab inherited the throne from his father, Jeroboam, during the second year of Asa's rule over Judah. Commentators agree that this exact timing is the result of a simple calculation of their predecessors' time in power. Jeroboam ruled for twenty-two years. Meanwhile, in the Kingdom of Judah, the combined reigns of Rehoboam and Abijam lasted exactly twenty years. This means Asa took the throne during Jeroboam's twentieth year. Consequently, when Jeroboam died two years later, his son Nadab stepped into power precisely during Asa's second year.

Nadab's own rule is recorded as lasting for two years. However, these were not two complete, full years. Instead, they were partial years that overlapped with the second and third years of Asa's reign [רש״י, מצודת דוד]. The primary approach among commentators is that the biblical method for counting royal timelines treats any fraction of a calendar year as a full year of reign for both the outgoing king and the incoming king. Because Nadab was killed and replaced by Baasha before completing his final year in power, that specific year was credited to both of their official records. This system of overlapping partial years is the key to resolving many apparent chronological contradictions found throughout the historical records of the kings of Israel and Judah [רלב״ג, אברבנאל].