When considering whether to upgrade to a new, more fuel efficient car, it's natural to think you will ultimately save money in the long run. We have developed a fuel economy comparison calculator that will crunch the numbers and tell you just how long that long run is. Plug in the numbers for both your current and prospective car purchases along with the mpg you currently get and hope to get on both cars. Remember that, because of depreciation and the general costs associated with buying a new car vs keeping the car you have, gas mileage numbers will have to be quite high to make the comparison impressive. Of course, if you are a person who cannot put a price on eco-friendliness, you'll at least be able to see how long it will take to make a difference financially, if not only ecologically.