What happens if I go over my lease mileage?

You'll pay an excess mileage charge for every mile over your allowance when you return the car, at a per-mile rate stated in your contract, often somewhere around 15 to 30 cents. Those charges can add up quickly. If you'll be over, options include buying the car, which avoids the charge, or trading it in early if it has equity. It's usually cheaper to buy extra miles upfront than to pay overage later.