What the calculator shows
Enter the negotiated vehicle price, cash down, trade-in credit and the amount your state treats as taxable. The calculator adds sales tax and financed fees to the amount borrowed, then shows the payment, interest and payoff effect of extra payments.
Calculation method
Sales tax equals the entered taxable amount multiplied by the local combined rate. Amount financed equals vehicle price minus down payment and trade-in credit, plus sales tax and financed fees. Fixed monthly amortization uses the entered annual contract interest rate. The dated Federal Reserve G.19 average APR provides the editable starting reference.
Inputs to confirm
Use the buyer’s order for the taxable amount because states handle trade-ins and taxable fees differently. Enter the contract interest rate that drives scheduled payments, then compare the result with the lender’s payment and disclosed APR.
Worked amount-financed example
At the defaults, $45,000 price minus $5,000 cash down, plus $3,375 tax and $500 financed fees, produces $43,875 financed. At 7.14% for 60 months, the planned payment is $871.68. The tax result depends on the separately entered local taxable amount.
| Change | Amount financed | What to verify |
|---|---|---|
| Trade-in credit increases | Usually falls in this model | Local taxable-base treatment |
| Fees paid in cash | Falls if removed from financed fees | Buyer’s order |
| Longer term | Unchanged | Lower payment but higher total interest |
Build the amount financed before comparing monthly payments
Vehicle price is not the same as amount financed. Cash down, trade-in credit, the locally taxable amount, sales tax and financed fees all change the balance before interest begins.
The taxable amount is a jurisdiction-specific input
States differ on trade-in credits, rebates, fees and vehicle transactions. Enter the taxable amount from the buyer’s order or local rule instead of assuming tax always applies to the negotiated price. Registration and title charges remain outside unless included in financed fees.
Contract rate drives payment; disclosed APR supports comparison
The model amortizes the amount financed using the entered contract interest rate. A lender APR may be higher because it incorporates covered finance charges. The dated Federal Reserve value is a planning reference, not an approval or a promise that the contract rate and APR will match.
A longer term can hide a higher total cost
Extending the term usually lowers the required payment but leaves principal outstanding longer. Compare amount financed, monthly payment, total interest and payoff date together, and consider whether the loan balance could exceed the vehicle value.
| Figure | Calculator field | Document |
|---|---|---|
| Selling price and credits | Price, down payment, trade-in | Buyer’s order |
| Tax and financed fees | Taxable amount, rate and fees | Buyer’s order and local tax record |
| Rate and APR | Contract rate versus disclosure comparison | Retail installment contract |