How the calculator works

Every result on this site comes from the standard amortization formula used by banks, credit unions, and dealer finance systems worldwide. Here is exactly what happens to your numbers.

1. Amount financed

We start with the vehicle price, subtract rebates, add sales tax (calculated on the price either before or after trade-in and rebates, depending on your state's rule — you control the toggle), add fees, subtract your down payment and trade-in equity, and add any negative equity rolled over from a previous loan:

Amount financed = price − rebate + tax + fees − down payment − trade-in equity + negative equity

2. Monthly payment

Payment = r × PV ÷ (1 − (1 + r)⁻ⁿ) — where PV is the amount financed, r is the monthly interest rate (APR ÷ 12), and n is the number of months. At 0% APR, the payment is simply PV ÷ n.

3. Amortization

Each month, interest accrues on the remaining balance (balance × r). The rest of your payment reduces principal. Early payments are interest-heavy; late payments are principal-heavy. The schedule table shows this month by month, and the CSV export gives you the full table.

4. Extra payments

Any extra monthly amount is applied entirely to principal. The calculator runs the schedule both ways — with and without the extra payment — and reports the interest saved and how many months earlier the loan ends.

5. Affordability mode

The reverse calculation: given a monthly budget, APR, and term, we solve the same formula for PV (the loan you can support), then add your down payment to get the maximum vehicle price.

Assumptions and limits

• Fixed APR and equal monthly payments (standard amortized loans). Not for leases or balloon structures.
• Sales tax rules vary by state and country — confirm your local rule.
• All calculations run in your browser. We don't see, store, or transmit your inputs.