Whether your rental car is covered depends on the coverages included in your insurance policy. The liability coverage on your existing auto insurance policy should cover you when you drive other vehicles, and the same is true for medical expense coverage. If you have comprehensive collision coverage on your policy, it may cover repairs to the rental car or a replacement if it's stolen, but it won't cover the rental company's lost income. You should call your insurance agent to confirm the specifics of your policy before assuming that your coverage will transfer.