Albert Barnes Commentary 2 Samuel 24:13

"So Gad came to David, and told him, and said unto him, Shall seven years of famine come unto thee in thy land? or wilt thou flee three months before thy foes while they pursue thee? or shall there be three days` pestilence in thy land? now advise thee, and consider what answer I shall return to him that sent me." — 2 Samuel 24:13 (ASV)

Compare Ezekiel 14:13-21. The “seven” years of famine correspond with the “seven” years of famine in Genesis 41:27, Genesis 41:30, and with the same number of years in 2 Kings 8:1. But in Chronicles, it is “three years,” which agrees better with the “three” months and “three” days. The whole passage is amplified in Chronicles, which seems less like the original text than this one.