Your monthly car payment is set by three things: the amount you actually finance, the interest rate (APR), and the number of months you borrow for. It uses the same amortization formula as any loan — the trick with cars is knowing what really goes into the "amount financed".
Step 1: Find the amount financed
It isn't the sticker price. It's:
- Vehicle price + sales tax and fees
- − your down payment
- − any trade-in value
So a $32,000 car with $2,000 tax/fees, $4,000 down and a $3,000 trade-in is financed at $27,000.
Step 2: Apply the payment formula
M = P · [ r(1+r)n ] / [ (1+r)n − 1 ] — where P is the amount financed, r is the monthly rate (APR ÷ 12), and n is the number of months.
Example: finance $30,000 at 7% APR for 60 months. The payment works out to about $594/month, with roughly $5,600 paid in total interest. The Auto Loan Calculator does this instantly and shows the interest total.
How loan length changes everything
Same $30,000 at 7%:
- 36 months: ~$926/month, ~$3,330 total interest
- 60 months: ~$594/month, ~$5,640 total interest
- 72 months: ~$512/month, ~$6,860 total interest
A longer loan lowers the payment but you pay far more interest and stay "upside down" (owing more than the car is worth) for years, because cars depreciate faster than long loans pay down.
Avoid the classic mistakes
- Shopping by monthly payment instead of total cost — dealers stretch the term to hit a number.
- Loans longer than 60 months on a depreciating asset.
- Zero down payment, which guarantees negative equity from day one.
Not sure what fits your income? Read how much car you can afford, then sanity-check the loan with the Loan Calculator and your budget with the Loan Affordability Calculator.
Try it yourself
Run your own numbers in the free Auto Loan Calculator — instant, private, no sign-up.
Open the Auto Loan Calculator →Frequently asked questions
- How is a car loan payment calculated?
- With the standard amortization formula M = P[r(1+r)^n]/[(1+r)^n−1], where P is the amount financed (price + tax/fees − down payment − trade-in), r is the monthly rate (APR ÷ 12) and n is the number of months.
- Does a longer car loan mean a lower payment?
- Yes, but it is a trap: the monthly payment drops while total interest rises sharply and you owe more than the car is worth for longer. Keep car loans to 60 months or less if you can.
- What is the amount financed on a car?
- The vehicle price plus tax and fees, minus your down payment and any trade-in value. Interest is charged on this figure, not the sticker price.
- Should I put money down on a car?
- Yes. A down payment shrinks the loan, lowers total interest, and reduces the time you spend in negative equity. Around 20% down is a common target.
Related guides
How to Calculate a Mortgage Payment, Step by Step · 15-Year vs 30-Year Mortgage: Which Should You Choose? · How Does Loan Interest Work? · How Much Car Can I Afford? The 20/4/10 Rule