SumAuto Loan Calculator
Work out exactly what a car will cost you each month. Enter the vehicle price, your down payment, any trade-in value, the APR and the loan term, and see your monthly payment, total interest and total cost.
Your monthly car payment
How It Works
Your monthly car payment is set by four things: how much you borrow, the interest rate, and how long you take to pay it back. First the calculator works out the amount financed: the vehicle price minus your down payment and trade-in value. Then it applies the standard amortization formula, M = P × r(1+r)n / ((1+r)n − 1), where P is the amount financed, r is the monthly rate (APR divided by 12), and n is the number of monthly payments. With a 0% APR, the payment is simply the amount financed divided by the number of months.
A longer term lowers your monthly payment but raises the total interest you pay, because interest has more months to build up. A bigger down payment or trade-in cuts the amount financed, which lowers both the payment and the total interest. That is why the same car can cost thousands more or less depending on how you structure the deal.
Worked example: a $25,000 car with no down payment and no trade-in, financed at 7% APR over 60 months. The amount financed is $25,000, and the monthly payment comes to about $495.03. Over five years you pay about $4,701.80 in interest, for a total cost of about $29,701.80. Put $5,000 down instead and the payment falls to about $396.02 a month, with total interest of about $3,761.44.
Remember that the figures here are for the loan alone. Sales tax alone can add several hundred to several thousand dollars depending on your state, and most states charge it on the full price (some give a credit for trade-ins). Add tax, title, registration and dealer documentation fees to the price before you sign, or ask the dealer for an out-the-door quote.
Frequently Asked Questions
What is a good APR for a car loan?
It depends on your credit score and whether the car is new or used. Borrowers with excellent credit often qualify for the lowest advertised rates, while lower scores mean higher APRs. Always compare offers from your bank or credit union with the dealer's financing before you decide.
Is a 72-month car loan a bad idea?
It lowers your monthly payment, but you pay much more interest overall and you risk owing more than the car is worth for years, since cars lose value fastest in the first few years. A 48- or 60-month term is usually a better balance for most buyers.
Does this calculator include sales tax and fees?
No. Tax, title, registration and dealer fees vary by state and are not included in the payment shown. To estimate the full cost, add your state's sales tax on the purchase price plus local fees to the vehicle price before calculating.
How does a trade-in affect my payment?
Your trade-in value reduces the amount you need to finance, dollar for dollar. A $4,000 trade-in on a $25,000 car means you borrow $21,000 instead of $25,000, which lowers both your monthly payment and the total interest you pay.
What if I have 0% APR financing?
Some manufacturers offer 0% APR deals, usually on new cars for well-qualified buyers. With 0% APR there is no interest at all: a $25,000 loan over 60 months costs exactly $416.67 a month. This calculator handles 0% correctly.
Last updated: November 2026