John Gill's  Exposition of the Bible 

1 Kings 15:25

And Nadab the son of Jeroboam began to reign over Israel in the second year of Asa king of Judah, and reigned over Israel two years.

And Nadab the son of Jeroboam began to reign over Israel in the second year of Asa king of Judah,.... Before Baasha did:

and reigned over Israel two years, not two whole years; for he began in the second of Asa, and in the third of that king's reign Baasha slew him, and reigned in his stead, 1 Kings 15:28.