The 20/4/10 Car Buying Rule

The 20/4/10 rule is a simple car affordability guideline: put 20% down, finance for no more than 4 years, and keep total transportation costs near 10% of income.

Why the rule helps

It encourages a meaningful down payment, faster payoff, and a smaller car budget. This can reduce interest, negative equity, and monthly pressure.

Why it may need adjustment

Modern car prices, insurance costs, and local transportation needs can make the rule difficult. Still, if a car fails the rule by a wide margin, it deserves a careful second look.

Use it as a warning light

The rule is not perfect, but it can prevent overbuying. Compare it with your actual take-home pay, emergency fund, debt, and ownership cost.