Auto Loan Calculator

About this calculator

This calculator works out your monthly car payment, the total interest you’ll pay, and the full out-the-door price — factoring in the vehicle price, down payment, trade-in value, sales tax, fees, and your loan’s APR. Use it before you visit the dealership to set a realistic budget, or to compare two financing offers side by side.

How to read your results

The headline figures are your monthly payment and the total interest paid over the life of the loan. The amortization table below breaks down each monthly payment into its principal and interest portions, showing how the interest share shrinks as the balance falls. Two caveats: first, this calculator rolls taxes and fees into the amount financed — if you plan to pay them in cash at signing, add them to your down payment instead. Second, the sales tax here uses the “tax the difference” rule: tax is applied to the vehicle price minus the trade-in. This is standard in many U.S. states, but some states tax the full purchase price regardless of any trade-in. Check your state’s rule; if it taxes the full price, set the trade-in to 0 and treat its value as part of your down payment.

Worked example

Vehicle price 25,000 · down payment 2,000 · trade-in 1,500 · sales tax 8% · fees 500 · APR 6.9% · 60-month term.

Taxable base is 23,500 (price minus trade-in), producing 1,880 in sales tax. Amount financed comes to 23,880. Monthly payment is 471.73, and total interest over five years is 4,423.60 — bringing the total loan cost to 28,303.60. The out-the-door price (before financing) is 27,380.

Frequently asked questions

How is sales tax calculated when I have a trade-in?

By default the calculator taxes the price after subtracting the trade-in (“tax the difference”). This is common in many U.S. states, but some states apply tax to the full vehicle price regardless. Confirm your state’s rule — if it taxes the full price, enter 0 for the trade-in and fold its value into your down payment instead.

What is the out-the-door price?

The out-the-door price is the total you owe to drive the car away: vehicle price plus sales tax plus fees. It does not include your down payment or trade-in, which reduce what you borrow but not what the car actually costs.

Are taxes and fees financed or paid upfront?

This calculator rolls taxes and fees into the amount financed, which is the most common dealer arrangement. If you prefer to pay them in cash at signing, add those amounts to your down payment — the monthly payment and total interest will both fall.

Does a shorter loan term always save money?

Yes on total interest — a 48-month loan at the same rate costs less in interest than a 72-month loan. But shorter terms mean higher monthly payments, so weigh the monthly cash-flow impact against the interest savings before deciding.

What happens if my interest rate is 0%?

At 0% APR the level-payment formula would divide by zero, so the calculator uses a simpler rule: monthly payment equals the amount financed divided by the number of months. Manufacturer 0% deals are real, but confirm whether the zero-rate offer replaces a cash rebate — sometimes taking the rebate and a standard loan costs less overall.

How it's calculated

The calculator first derives the taxable base by subtracting the trade-in from the vehicle price (floored at zero), multiplies that by the sales-tax rate to get the sales-tax amount, then computes the out-the-door price as vehicle price plus sales tax plus fees. The amount financed is the out-the-door price minus the down payment and minus the trade-in, again floored at zero. The monthly payment uses the standard level-payment 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 term in months; at r = 0 the formula degenerates and the calculator falls back to M = P / n. Both the payment formula and the per-month amortization schedule are provided by the shared levelPayment and amortize functions in src/lib/finance.ts. Total interest is summed from the interest column of the schedule; total loan cost is the amount financed plus total interest. Sources: Bankrate auto loan calculator methodology, Edmunds simplified pricing model, and Investopedia amortization definition.