'Eighteenth' in the Bible

Now Jehoram the son of Ahab began to reign over Israel in Samaria the eighteenth year of Jehoshaphat king of Judah, and reigned twelve years.

And it came to pass in the eighteenth year of king Josiah, that the king sent Shaphan the son of Azaliah, the son of Meshullam, the scribe, to the house of the LORD, saying,

But in the eighteenth year of king Josiah, wherein this passover was holden to the LORD in Jerusalem.