When you're buying a new car, you might have to choose between a rebate and special dealer financing. We can help. First, type in the interest rate and the rebate amount the dealer is offering you. Next, type in the regular rate you'll get on a car loan if you don't go through the dealer. If you don't know the best car loan rates in your area, find them here at Bankrate.com. After that, enter the purchase price of the vehicle. Then, write in your down payment. Finally, enter the loan term (for example, 36, 48 or 60 months). Now type in the rate earned on savings if you put the rebate into a one-year CD. (Find the best CD rates here). Then add up the federal and state taxes you'll pay on the money you'd earn from a CD. For example, if you're in the 28 percent federal tax bracket and you have a 5 percent state income tax, put in 33. Finally, click on whether your rebate is invested in savings or added to your down payment. Press the bar at the bottom and we'll do the rest.