How much car can you afford to finance? Try the 20-4-10 rule

Several analysts have reported that car sales are expected to rise this year, in part because there’s a sizeable group of people who need to replace their older vehicles. But how much is the “right” amount to spend?

If you’re looking to finance, you might consider the 20-4-10 rule: 20 percent down; financing that lasts no longer than four years; and principal, interest and insurance that doesn’t exceed 10 percent of your gross household income.

It’s a formula that can help change the way we think about how we define the affordability of a car, and potentially start to free up some extra cash for other, more important financial needs such as retirement or even the more basic emergency savings fund.

“How that change in thinking lowers your stress level is just amazing,” says Mike Sante, a managing editor at Interest.com, which recently completed a study that looked at car affordability. “It can make a tremendous change in your quality of life. This is where the money is for your savings.”

Americans are largely spending too much on cars, an asset that is often our second-largest household expense after rent or a mortgage and offers no potential for increasing net worth. For example, taking into account car insurance costs and the Boston area’s median income of almost $70,000 a year, Interest.com calculated that a typical Boston household can afford to spend up to $26,025 on a car. It would take a pretty good amount of self-control to avoid spending more than that, since the average new car with bells and whistles costs $30,550.