If you paid all the costs upfront, it makes no difference to turn it in early. You may want to figure if the overage cost ( typically 20 or 25 cents a mile, check your lease ) is lower cost for the mileage you need, as that would be the only added cost if you keep it for another year. My lease was 20 cents a mile, or 2K per 10K miles, not really a bad deal for another year of using the vechile. Keepin another year also means no sales tax, dealer fees ect.