THE NUMORIX GUIDE
How to use the Auto loan calculator
Last reviewed September 14, 2026
What this calculator does
The price-to-payment mode builds the financed balance as price minus incentives, down payment, and trade-in equity, plus trade-in debt and, when selected, sales tax and fees.
Formula and method
The price-to-payment mode builds the financed balance as price minus incentives, down payment, and trade-in equity, plus trade-in debt and, when selected, sales tax and fees. Tax is applied to the price, or to price minus trade-in in most states; the engine uses the price alone for California, the District of Columbia, Hawaii, Kentucky, Maryland, Michigan, Montana, and Virginia. A monthly amortization formula then splits each payment into interest and principal. The payment-to-price mode solves the supported principal from a target monthly payment.
Variables and inputs
Use vehicle price, term in months, annual interest rate, cash incentives, down payment, trade-in value, trade-in amount owed, state, sales-tax rate, fees, and the include-costs choice. In payment mode, monthly payment is the target instead of a price to solve against. Dollar fields are dollars, term is months, and rates are percentages.
Worked example
Suppose the price is $30,000, incentives are $1,000, down payment is $3,000, trade-in value is $5,000, trade-in debt is $2,000, New York tax is 8%, and fees are $600. Taxable price is (30,000 - 5,000) x 0.08 = $2,000. With costs included, the loan is 30,000 - 1,000 - 3,000 - 5,000 + 2,000 + 2,000 + 600 = $25,600; at 0% for 60 months the payment is 25,600 / 60 = $426.67.
How to interpret the result
The monthly figure reflects the deal inputs, not only the vehicle sticker price. Trade-in equity reduces borrowing, while a trade-in payoff increases it. Compare total payments and total cost as well as the monthly amount because a longer term can make a vehicle appear cheaper each month.
Common mistakes to avoid
Enter the amount still owed on the trade-in rather than the original loan amount. Do not subtract the trade-in value twice. Check whether the tax base in the state and the dealer's fee treatment match the transaction documents before comparing offers.
Assumptions and limitations
State tax treatment is simplified to the fixed list in the engine and does not model local taxes, rebates with tax consequences, registration, title charges, add-ons, or lender-specific fees. Payment mode resets deal adjustments and is a principal estimate, not an approval limit.