This popular car-buying rule isn't realistic for most Americans—here's the income needed to make it work

For years, financial planners have recommended a simple rule of thumb to help drivers avoid taking on too much car debt. The so-called 20-4-10 rule suggests buyers put 20% down, finance a vehicle for no more than four years and keep total transportation costs below 10% of their gross income. The guideline is meant to keep transportation costs manageable, limit interest expenses and reduce the risk of owing more on a vehicle than it's worth since cars typically depreciate over time. However, for many buyers, the rule no longer reflects reality, financial planners say. "The 20-4-10 rule isn't wrong. It's calibrated for a car market that no longer exists," says Jeff Judge, a certified financial planner at Chesapeake Financial Planners. In fact, few buyers follow the rule's four-year financing recommendation today: Just 5.6% of new-vehicle loans had 48-month terms, according to a 2025 analysis by Edmunds. And the math has only gotten tougher in recent years, with average new vehicle prices in April climbing to about $49,461 while the average used vehicle is listed for about $26,300 , according to Cox Automotive. Even for buyers trying to save money by shopping used, following the rule can require a six-figure income. New-car buyers would need to earn even more. Why the rule is unrealistic for the typical car buyer For many buyers, the 10% transportation-cost guideline is the hardest part of the rule to follow. …