Albert Barnes Commentary 2 Kings 24:12

"and Jehoiachin the king of Judah went out to the king of Babylon, he, and his mother, and his servants, and his princes, and his officers: and the king of Babylon took him in the eighth year of his reign." — 2 Kings 24:12 (ASV)

The eighth year - Jeremiah calls it the seventh year (Jeremiah 52:28), a statement which implies only a different manner of counting regnal years.