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Auto Loan Calculator
Estimate your monthly car payment, total interest, and payoff date — including down payment, trade-in, and sales tax.
Where your money goes
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What is an auto loan calculator?
An auto loan calculator turns the dealership's numbers into a payment you can actually compare. Most car ads show a flashy monthly figure with a footnote of fine print: down payment required, taxes and fees not included, qualified buyers only. This tool flips it around. You enter what you're really paying — the sticker price, the down payment, your trade-in credit, and the sales tax in your state — plus the term and APR a lender quoted, and it returns the honest monthly payment along with the total interest and the date you'd actually own the car. Behind the scenes it uses the standard fixed-rate amortization formula that every bank and credit union runs internally, so the result matches the contract within rounding. Use it to compare two financing offers, decide whether a longer term to lower the payment is worth the extra interest, or check whether a 0% promotion really beats a cash rebate. Everything runs in your browser — no email, no credit pull, no upsell.
How to use it
- Enter the vehicle price — Use the negotiated out-the-door price before tax, not the manufacturer's suggested retail price.
- Add your down payment and trade-in — Both reduce the amount you finance. If you don't have a trade-in, leave it at zero.
- Set the sales tax rate — Most US states roll sales tax into the loan. Use your state's combined rate; leave it at 0 if your jurisdiction handles tax separately.
- Pick the term — Common terms are 36, 48, 60, 72, or 84 months. Longer terms drop the payment but multiply the total interest.
- Enter the APR — Use the rate the lender quoted you. If you only have a teaser rate, run the math at a realistic rate too.
How the math works
Two steps. First we figure out the amount being financed — the price, minus your down payment and trade-in, multiplied by (1 + the sales tax rate). Then we apply the standard fixed-rate amortization formula to get the level monthly payment that fully repays the loan over the term.
P = (price − down − trade-in) × (1 + tax%/100)
M = P × [ r(1+r)n ] / [ (1+r)n − 1 ]
Where r is the monthly rate (APR ÷ 12 ÷ 100), n is the number of months, and M is the monthly payment.
Why a longer term costs more
Stretching from 60 months to 84 months can drop the monthly payment by 25-30%, but the total interest typically rises 60-80% — because you're paying interest on a much higher balance for two extra years. Longer terms also raise the chance of being upside-down (owing more than the car is worth) when you eventually trade it in.