You enter your mileage, and the calculations take low or high mileage into the figures given. If you also get a good discount on the X5, you will be lucky to get full average trade-in value, unless your car is perfect. If you are paying list or close to it, they are making about $8000 profit on the 4.4, and should give you a fairly good value for your car. Hey, they make money on both cars, and they try to make the most money they can.