Auto Loan Calculator
Calculate monthly car payment, total interest, and total cost. Supports trade-in, sales tax, and down payment.
What this calculates
Auto loans look simple on the dealer's sheet but quietly bury sales tax, fees, and negative equity into the payment. This calculator separates the components so you can see what you're really borrowing — vehicle price, less trade-in, less down payment, plus tax — and what your monthly payment, total interest, and total cost will be over the term.
Formula & how it works
Loan principal = (price − trade_in − down) × (1 + sales_tax_rate). Monthly = P × r × (1+r)^n ÷ ((1+r)^n − 1), where r is the monthly rate and n is months. Total paid = monthly × n. Total interest = total paid − loan principal. Negative equity from a trade-in (when you owe more than the trade is worth) gets rolled into the new principal — that's the trap.
Worked example
$30,000 car, $3,000 trade-in, $2,000 down, 7 % sales tax, 6.5 % APR, 60 months. Pre-tax balance = 30 000 − 3 000 − 2 000 = $25,000. With tax = 25 000 × 1.07 = $26,750. Monthly at 6.5 %/60 = $523. Total paid = $31,400. Total interest = $4,650.
Frequently asked questions
What's a reasonable car-loan term?
36–60 months keeps interest reasonable and prevents being underwater. 72–84 month loans are common but expensive — you'll often owe more than the car's worth for the first 3–4 years.
Should I take dealer financing or my own?
Get pre-approved from your bank or credit union first. Then negotiate the car price as a cash buyer. If the dealer beats your pre-approved rate, take it — but only because you knew your alternative.
What's gap insurance?
Covers the difference between what you owe and what your insurer pays if the car is totaled or stolen. Worth it on long-term, low-down-payment loans where you'll be underwater for years.
How does APR differ from interest rate?
APR bundles fees into the effective rate. A 6 % rate with $800 of fees might be a 7 % APR. Always compare APR, not the headline rate.
Disclaimer: Informational only — verify all numbers with your lender.