Does your car insurance end the day you cancel or are you still covered for 30 days?

The expiration date, or the day you cancel is the official end of insurance coverage. Period. The 30 day "grace" period is a myth. If you just let the policy expire by not paying the renewal premium, they will PROBABLY reinstate your coverage retroactive to the expiration date, but I would not rely on that. If you CANCELLED, that's the end of your coverage.