In deciding whether to put a major expense into a car, what is the value of being the original owner of a car and keeping it, as opposed to buying a used car? If you're the original owner, you generally know every thing about the car's maintenance, something you can never be 100% confident about when buying used. I am trying to calculate whether it is worth it to put money into a car and keeping it for several more years, or trading it in, and to me there should be some factor as to what a car is worth if you're the only registered owner. Is it worth 20% more than book value? 15%? 10%?