A great app if you want to track your gas mileage is gas cubby, you can keep track of your fill-ups, how much you paid, amount you put in etc. Then it breaks down everything calculates gas mileage, how much you spent in total, miles driven per day, cost per mile, plenty. They've got both a free and pay app. I think the pay app allows you to sync it quickbooks or something in addition to being ad-free