<prompt> Human: My father in-law is always telling me to trade up before my car loses value. He said thats the smartest way and leads to lower total cost of ownership.But Ive read that running your car into the ground and buying new each time is the most cost effective method.Ive read both arguments:A Trading up often you dont have huge repair bills to deal with because they are under warranty and newer cars or more fuel efficient. B If you run your car into the ground, you can amortize the cost of the car over many years.I know there are other factors like happiness and that newer cars have better safety features more airbags, crash avoidance etc. etc.. But from a purely financial standpoint, which philosophy will let me keep the most wealth in a lifetime? Has anyone ever looked at the numbers?  <response>: Too many variables, you dont know at the start. But a car depreciated the most when its new, so trading it in because it still has value means you get hit with the depreciation the most.But what works for me: Buy a 6-7 year old car with 60.000 - 70.000 miles that has depreciated to a point it only cost 13 of the original price.New enough that it still fairly good in crash tests, shouldnt have rust issues and not enough miles to be worn. Old enough that the cost of the car and insurance is low. Not sure why people thing cars will suddenly fall apart after the warranty runs out. The best way is to do all manufacture recommended service intervals and fix things when they start to give issues. Most break down come with lots of warnings. I do this and never actually had a break down. 