What is the 20/4/10 rule for buying a car?

It is a rule of thumb: put at least 20 percent down, finance for no more than four years, and keep total monthly car costs, including insurance, under 10 percent of your gross income. It is meant to keep you from owing more than the car is worth and from overspending. Many buyers can't meet all three today, so treat it as a guide, and aim to get as close as you comfortably can.