Q: WHAT YEAR DID REHOBOAM BEGIN HIS REIGN IN JUDAH?
A: IT DEPENDS WHAT CALENDAR YOU ARE USING!
On the Gregorian calendar (the one you might have on your wall) the year was 918 BC.
On the Hebrew calendar, sometimes called the biblical calendar, the year was 3129AM.
1 Kings 14:21 – And Rehoboam the son of Solomon reigned in Judah. Rehoboam was forty-one years old when he became king. He reigned seventeen years in Jerusalem, the city which the Lord had chosen out of all the tribes of Israel, to put His name there. His mother's name was Naamah, an Ammonitess.
All of 1 Kings 14.
Jeroboam Began 22-Year Reign (Israel)
1 Kings 14:20 New King James Version (NKJV)
20 The period that Jeroboam reigned was twenty-two years. So he rested with his fathers. Then Nadab his son reigned in his place.