The installment formula
How to Calculate an Auto Loan Payment
How to calculate an auto loan, on a typical U.S. dealer contract, means how to calculate the payment: the same dollar amount each month if the APR and the term do not change. You do not need a lender’s worksheet to see how that number is built. You need four inputs and a clear order of operations. The Auto Loan Calculator runs that math in the browser once you enter the numbers.
Start with the amount financed
The payment is not calculated on the sticker alone. It is calculated on the amount financed: vehicle price minus cash down minus the net trade-in credit. If you still owe money on the trade-in, only the net credit reduces the new loan. A $32,000 price, a $4,000 down payment, and no trade-in leaves $28,000 to finance.
Sales tax, title, registration, and documentation fees are not in that subtraction unless you add them to the price first. That is a separate question, covered in whether taxes and fees are included in a car loan.
Turn APR into a monthly rate
APR is an annual percentage rate. For a monthly payment you divide that rate by 12. A 6.49 percent APR becomes about 0.5408 percent per month (6.49 ÷ 12). You enter the yearly APR on this site, not the monthly rate. The calculator does the division.
A lender’s disclosed APR can include certain fees. This walkthrough, and the calculator, treat the APR you type as the rate in the payment formula. They do not rebuild a Truth in Lending disclosure from a pile of dealer add-ons.
Why the payment is the same every month
On a standard amortizing loan, each payment covers that month’s interest on the remaining principal and then reduces the principal. Early payments are heavier on interest. Later payments are heavier on principal. The dollar amount you send does not change if you stay on schedule.
When the APR is above zero, that fixed amount comes from the usual U.S. installment formula: the amount financed, the monthly rate, and the number of months. When the APR is 0 percent, there is no interest to allocate. The payment is the amount financed divided evenly across the term.
A worked example you can check
Take $28,000 financed at 6.49 percent APR for 60 months. That loan’s estimated payment on the Auto Loan Calculator is $547.72. Sixty payments total $32,863.26. Subtract the $28,000 principal and the estimated interest — the finance charge — is $4,863.26. That interest is already inside the $547.72. It is not a second monthly bill.
At 0 percent APR, an $18,500 loan for 36 months is $513.89 a month. Interest over the term is $0.00. If you want the finance charge called out as a share of the payments, use the Auto Loan Interest Calculator.
What this formula is not
It is not an add-on interest loan, where a finance charge is tacked on up front and then split. It is not a simple-interest daily payoff schedule, though paying extra principal still saves interest in real life. It is not a lease money factor. And it is not a quote. Insurance, fuel, and maintenance sit outside the installment.
A longer term usually lowers the monthly payment and raises the interest if you keep the loan to the last month. Change only the term on the calculator if you want to see that trade-off without inventing a new price.
Payment-formula questions
How do you calculate an auto loan payment by hand?
Find the amount financed, divide APR by 12, then apply the amortizing installment formula for that many months. Or enter the same numbers on the Auto Loan Calculator and read the payment.
Does a longer term change only the payment?
No. The monthly amount usually falls. The finance charge usually rises if you make every scheduled payment. Compare two terms with the same price and APR.
Open the calculators
- Auto Loan Calculator — estimate the monthly payment from price, APR, term, down payment, and trade-in.
- Auto loan interest — the same loan with the finance charge stated as a percent of the payments.