<prompt> Human: My wife and I have been looking at buying a new car. She currently has a 2006 model, which after getting married, I realized she is paying 9.5 interest. It was her first car. Anyway, she has 2.5 years left on the loan, with slightly over 5000 left. The car has 75,000 miles on it, and otherwise is in good mechanical condition. She just took a new job that is a bit longer of a commute, so fuel mileage has become a concern, as her current car only gets 20mpg. We started looking at a new Prius. Toyota is offering 0 for 60 months on new models. So the question, should we look at doing this? Considering that she owes 5000 on her current car, which is already creeping up in mileage, and her need for a reliable and efficient vehicle. I am worried that by the time we have the car paid off, it will have high mileage, be 10 years old, and be close to needing replacement. Or, we can trade it in, and get a brand new Prius. With 0 financing, it would come out with a payment of about 200 more per month, but when its paid off, we will have a car with 60,000 miles, and a solid 5 more years of service.Another factor is fuel costs. Being conservative, we estimate that we will save at least 100 per month in fuel costs. A snap shot of our financial situation.Combined income: 100,000Debt: Auto Loan: 5000Student loans: 56,000MortgageNo Credit card debt.We save 10 of our gross income, and are on track to pay off our student loans in 5 years. We both match our 401ks.Is the 0 something we should consider? Also, I have looked at used Priuss. They dont have the available financing or warranty, with only 3-4k in savings. The warranty is worth it in my opinion, and the 0 makes up for it. I guess Im looking for justification, or a stern warning as to why its a dumb idea.  <response>: Where are you getting the idea that a car should be replaced at ten years? There will be some maintenance required, and you can look that up in the book, but that five grand is going to be a much more cost-effective approach than continually buying new cars just because the old one is getting a bit aged. What is your monthly payment and how much would it be for the Prius? Additionally, what is the KBB on the car? Would you even be able to sell the current car for enough to pay off the 5k or would you be adding the extra to the price of your Prius loan? You really need to sit down and run the numbers on everything; factor in how much you could sell the car for, the monthly cost of the Prius vs current car, and cost of mileage estimated per month. You can use this information to determine how long it will take for the Prius to save you money instead of costing you.Just a heads-up; I would NOT factor in the resale price or age of the vehicle. Those are non-issues and should not be used as an argument to get a new car, because those are problems that every car has--even if you buy a Prius now youll run into the issue with it eventually as well. Cars should really only be replaced, from a financial standpoint, once a car costs more to repair and maintain and drive than a replacement would. There are other reasons to replace a car, such as usage reasons like suddenly a 2-door is inadequate when youve got kids, etc., but from a financial standpoint thats it--which one cost you more, current or new. 