A car is one of the biggest purchases most people make, and a low advertised payment can hide a high total cost. The 20/4/10 rule is a simple guideline for keeping car ownership affordable.
What the rule says
- 20%: put at least 20% down. A large down payment reduces what you borrow and helps you avoid owing more than the car is worth as it depreciates.
- 4: finance for no more than 4 years (48 months). Shorter loans cost far less interest.
- 10%: keep your total monthly transportation costs, including the loan payment, insurance and fuel, under 10% of your gross monthly income.
Worked example
Suppose you earn $60,000 a year, which is $5,000 a month before tax. Ten percent is $500 a month for everything to do with the car. If insurance and fuel come to about $250, that leaves $250 for the loan payment.
At a 7% APR over 48 months, a $250 payment supports a loan of about $10,440. If that is 80% of the price (you put 20% down), the car can cost roughly $13,000. That is a modest car, and it shows how strict the rule is.
Is the rule realistic?
Many buyers do not follow it, especially with today's vehicle prices. Loans of 60 to 72 months are common. The rule is best treated as a conservative benchmark. If you stretch it, know the trade-offs:
- Longer terms lower the monthly payment but increase total interest.
- A small down payment can leave you owing more than the car is worth for the first few years.
- Higher payments reduce the money available for saving and emergencies.
Use the auto loan calculator to compare terms side by side, then work out what fits your budget.
Costs that the monthly payment leaves out
- Insurance, which can vary a lot by age, location and vehicle.
- Fuel or charging, which depends on how much you drive.
- Maintenance and repairs, including tires and brakes.
- Registration, taxes and fees, which recur each year.
- Depreciation, the largest cost of owning a new car, even though you never write a check for it.
Ways to lower the cost
- Consider a well-maintained used car, which has already taken its biggest depreciation hit.
- Get pre-approved by a bank or credit union before visiting the dealer.
- Negotiate the total price rather than the monthly payment.
- Save up a larger down payment if you can wait.
This article is general information, not financial advice.