2 Samuel 2:11 (BSB)

And the length of time that David was king in Hebron over the house of Judah was seven years and six months.

From 2 Samuel 2. Also in the ESV.

Commentary on 2 Samuel 2:11

• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on 2 Samuel 2:8-17: Here is, I. A rivalship between two kings - David, whom God made king, and Ishbosheth, whom Abner made king. One would have thought, when Saul was slain, and all his sons that had sense and spirit enough to take the field with him, David would come to the throne without any opposition, since all Israel knew, not only how he had signalized himself, but...
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on 2 Samuel 2:11: And the time that David was king in Hebron over the house of Judah,.... And over them only: was seven years and six months; to which being added thirty three years he reigned over all Israel in Jerusalem, made forty years and six months; and which, for the roundness of the number, is usually called forty years. See Sa2 5:4.
• Geneva Bible Notes (Reformed), Geneva Bible Study Notes on 2 Samuel 2:11: And the time that David was king in Hebron over the house of Judah was seven years and six months. (g) After this he reigned over all the country 33 years, .
• Keil & Delitzsch (Lutheran), Biblical Commentary on the Old Testament on 2 Samuel 2:10-11: 2Sa 2:10-11 Length of the reigns of Ishbosheth over Israel, and David at Hebron. The age of Ishbosheth is given, as is generally the case at the commencement of a reign. He was forty years old when he began to reign, and reigned two years; whereas David was king at Hebron over the house of Judah seven years and a half.