King Zechariah reigned over Israel for only six months, and here is why,
“Now the rest of the acts of Zechariah, indeed they are written in the book of the chronicles of the kings of Israel. This was the word of the LORD which He spoke to Jehu, saying, ‘Your sons shall sit on the throne of Israel to the fourth generation.’ And so it was” (2 Kings 15:11-12).
Zechariah, like those before him, was evil, and so his reign ended shortly, and the house of Jehu ended with the death of this king.
The Lord says what He means and means what He says.