How much car can you afford? The 20/4/10 rule

A car is one of the easiest ways to overspend, because dealers quote you a monthly payment, not a total cost — and a payment you can technically make is not the same as a car you can actually afford. A simple, widely used guardrail keeps you honest: the 20/4/10 rule.

The 20/4/10 rule

• 20% down. Put at least 20% down (cash or trade-in). This shrinks the loan and keeps you from being "underwater" — owing more than the car is worth, which happens fast because cars depreciate quickly.
• 4-year loan, maximum. Finance for no more than 48 months. Longer loans (72–84 months) are how people end up owing money on a car worth far less, and they pile on interest.
• 10% of income. Keep your total monthly vehicle costs — loan payment plus insurance, and ideally fuel and maintenance — under 10% of your gross monthly income.

A worked example

Why the term matters so much

Stretching the loan is the most common way people fool themselves. A longer term lowers the monthly payment, which feels affordable, but it increases total interest and — because the car depreciates faster than you pay down the loan — keeps you underwater for years. If something happens to the car, or you need to sell, you owe more than it is worth. A 48-month cap is what keeps your loan balance roughly in line with the car's value.

The full cost of a car

The payment is only part of it. Budget for the whole picture, or the "affordable" car will not feel affordable: insurance, fuel, routine maintenance, tires, registration, and repairs as it ages. The 10% guideline is meant to cover the payment and insurance; keep some room for the rest.

The bottom line

Put 20% down, finance for four years or fewer, and keep total vehicle costs under 10% of your income. It is a conservative rule on purpose — a car is a depreciating asset, and the goal is reliable transportation that leaves your budget intact, not the most car a lender will approve. Work backward from a payment you can afford using the auto loan calculator, and let that set your price range.

Educational information only, not financial advice. Figures are illustrative and exclude taxes and fees.