'Forty Years' in the Bible

Ish-bosheth, Saul's son, was forty years old when he began to reign over Israel, and he reigned two years. But the house of Judah followed David.

David was thirty years old when he began to reign, and he reigned forty years.

And it came to pass at the end of forty years, that Absalom said to the king, I pray thee, let me go and pay my vow, which I have vowed to LORD, in Hebron.