When does a car warranty start?

A factory warranty starts on the vehicle's in-service date, which is usually the day it was first sold or delivered to a retail buyer, or the day it was first used as a demo, loaner or fleet vehicle. That means a new car that sat on a lot still has its full warranty when you buy it, but a dealer demo may already have used some. You can ask the dealer or a brand dealership's service department to look up the in-service date by VIN.