3 Reasons a Chainsaw Chain Keeps Coming Off

Chain tension is too loose A chainsaw chain should be snug against the bottom of the bar rail with no sag, but still able to spin freely by hand. Tighten it first.

Bar rails are worn or damaged A burred or pinched rail lets the chain wander off track. Inspect the rails and file or replace them if needed.

Drive sprocket at the tip is worn A worn sprocket gives the chain extra room to jump. Replace it if the teeth are sharp or uneven.