A car is one of the biggest purchases most people make without a spreadsheet — and it's easy to walk out of a dealership with a payment that quietly wrecks your budget for years. One simple framework keeps that from happening: the 20/4/10 rule.
The 20/4/10 rule
- 20% down. Putting at least 20% down reduces how much you finance and helps you avoid owing more than the car is worth (being "underwater") as it depreciates.
- 4-year loan, max. Financing for no more than 48 months keeps the loan term roughly in line with how fast the car loses value.
- 10% of gross income. Many advisors suggest keeping the loan payment itself under about 10% of your gross monthly income — and total transportation costs (loan, insurance, gas, maintenance combined) under roughly 15-20%.
It's a guideline, not a legal limit — but it's a fast way to catch a payment that looks fine in isolation and terrible next to everything else in your budget.
What that looks like in real payments
Here's the estimated monthly loan payment at a 7% APR over 4 years, assuming a 20% down payment:
| Car price | Financed (80%) | Est. monthly payment |
|---|---|---|
| $15,000 | $12,000 | $287 |
| $20,000 | $16,000 | $383 |
| $25,000 | $20,000 | $479 |
| $30,000 | $24,000 | $575 |
| $35,000 | $28,000 | $670 |
| $40,000 | $32,000 | $766 |
Using the 10% guideline, a $479/month payment on a $25,000 car fits comfortably under a gross monthly income of about $4,800 — roughly a $57,500 salary. Run your own price, down payment and term for an exact number.
Why 4 years, not 6 or 7?
Stretching a loan to 6 or 7 years lowers the monthly payment, which is exactly why dealers like offering it — but it comes with real costs: far more total interest paid over the life of the loan, and a longer stretch where you likely owe more than the car is worth, since cars depreciate faster than a 6-7 year loan pays down. A shorter term costs more per month but far less overall, and gets you to full ownership while the car still has real value.
See the exact numbers for your price point
For a full rate-and-term table on a specific loan amount, check the payment breakdown pages:
Frequently asked questions
What percent of income should go to a car payment?
A common guideline is keeping the loan payment itself under about 10% of your gross monthly income, with total transportation costs (payment, insurance, gas, maintenance) under roughly 15-20%.
Is a 6-year car loan a bad idea?
It lowers the monthly payment, but you'll pay significantly more total interest and spend longer owing more than the car is worth, since cars depreciate faster than a 6-7 year loan amortizes. A 4-year term or shorter is generally safer.
How much down payment do I need on a car?
20% is the widely-used benchmark. It reduces the amount financed, lowers your payment and interest, and helps avoid being underwater on the loan early on.
