How Car Loan Interest Works
What determines your car loan APR, why used cars cost more to finance, and how stretching the term to a lower payment can nearly double the interest you pay.
The short version
- Your APR depends mostly on your credit score, whether the car is new or used, and the loan term.
- Used-car loans cost more — recent averages are about 6.4% for new vs. 11.4% for used.
- A longer term lowers the payment but raises total interest — 84 months can nearly double it vs. 48.
- Longer loans also keep you “underwater,” owing more than the car is worth, for years.
A car loan looks simple: borrow a price, pay it back monthly. But the interest rate and the length of the loan quietly decide how much the car really costs you — sometimes thousands of dollars more than the sticker. Here’s how the interest works and where it gets expensive.
What sets your rate
Your APR is priced on risk. Three things move it most:
- Credit score — the single biggest factor. Well-qualified buyers get single-digit rates; subprime borrowers routinely pay 13%–16% or more.
- New vs. used — used cars carry higher rates. Recent averages run about 6.4% for new and 11.4% for used, because used cars are riskier collateral.
- Loan term — longer loans often carry slightly higher rates, and always cost more in total interest.
The longer-term trap
Dealers love to quote a lower monthly payment, and the easy way to get one is to stretch the loan out. It works — but the interest cost balloons. Here’s the same $30,000 loan at 7%, at different lengths:
| Loan term | Monthly payment | Total interest |
|---|---|---|
| 48 months | $718 | $4,483 |
| 60 months | $594 | $5,642 |
| 72 months | $511 | $6,826 |
| 84 months | $453 | $8,034 |
Going from 48 to 84 months drops the payment by $265 — but nearly doubles the interest, from about $4,500 to $8,000. You pay less each month and far more overall.
Being “underwater” is the other cost
A long loan can leave you owing more than the car is worth
Cars lose value faster than a long loan pays down. On a 72- or 84-month loan you can spend years “underwater” — if the car is totaled or you want to sell, you owe more than you’d get back. A bigger down payment and a shorter term are the fix.
How to pay less interest
- Improve your credit before you shop — even a small score bump can drop your rate a full point.
- Choose the shortest term whose payment you can comfortably afford.
- Put more down, so you finance less to begin with.
- Get pre-approved from a bank or credit union so you can compare against the dealer’s offer.
Run the numbers first
Compare the monthly payment and total interest across rates and terms before you set foot in the showroom.
Not sure how big a loan fits your budget in the first place? Start with what you can afford.
Sources
This article is for general education and is not financial, tax, or legal advice. Figures reflect published 2026 IRS and SSA amounts as of the date above; verify current limits with the linked sources or a qualified professional before acting.
About the author
David Miles is the founder of FigureMoney and builds independent, source-backed personal-finance tools across the Modern Site Builders network. Every calculator and guide cites the IRS, SSA, or primary research behind its numbers.
Calculators in this guide
Auto Loan Calculator
Free auto loan calculator. Estimate your monthly car payment from price, down payment, trade-in, sales tax, APR, and term, with total interest and payoff.
Car Affordability Calculator
Find out how much car you can afford. Enter your monthly budget, down payment, trade-in, tax, APR, and term to see the maximum vehicle price.
Personal Loan Calculator
Estimate the monthly payment, total interest, and total cost of a personal loan from the loan amount, interest rate (APR), and term.
Keep reading
How Much Car Can You Afford?
Dealers sell you a monthly payment; your budget cares about the total cost. Here’s a simple rule for setting a car budget — and the costs people forget to count.
How Much Should You Put Down on a Car?
A down payment does three things at once: shrinks your payment, cuts your interest, and keeps you from owing more than the car is worth. Here’s how much to aim for.