John Gill Commentary 1 Kings 16:10

"and Zimri went in and smote him, and killed him, in the twenty and seventh year of Asa king of Judah, and reigned in his stead." — 1 Kings 16:10 (ASV)

And Zimri went in and smote him, and killed him
When in his drunken fit: and this was

in the twenty seventh year of Asa ;
when Elah had not reigned two full years:

and reigned in his stead ;
that is, Zimri; his reign was short indeed, but seven days, (1 Kings 16:15) .