מלכים א, פרק ט״ו, פסוק כ״ח

Political power in the ancient kingdom could change hands swiftly and violently. The assassination of Nadab and the sudden rise of Baasha to the throne took place shortly after Nadab's reign began.

The timeline of this overthrow is tracked alongside the rule of Asa, the king of Judah. Baasha struck down Nadab during Asa's third year in power. Since Nadab only assumed control during Asa's second year, commentators agree that his officially recorded two-year reign does not mean he ruled for two full years. Rather, he held power for just a portion of Asa's second year and a portion of his third. In the historical record, these two partial, broken periods are simply combined and counted together as his two years of kingship.