Albert Barnes Commentary Jeremiah 25:1

"The word that came to Jeremiah concerning all the people of Judah, in the fourth year of Jehoiakim the son of Josiah, king of Judah (the same was the first year of Nebuchadrezzar king of Babylon,)" — Jeremiah 25:1 (ASV)

The fourth year - See (Daniel 1:1) note. This invasion of Judea, in which Daniel was carried captive to Babylon, was according to official dating the fourth, but according to actual time the third, year of the Jewish king. Nebuchadnezzar was not yet fully king, but associated with his father Nabopolassar.