Auto Loan Calculator

Auto financing has more moving parts than a plain installment loan because the amount financed often starts with a vehicle price, sales tax, and down payment or trade-in allowance. This calculator estimates the monthly payment, sales tax, total cost, total interest, total payment, and payment count for a financed vehicle purchase. For a generic borrowing scenario without tax or down payment, use the loan calculator. For unsecured borrowing, use the personal loan calculator. For depreciation after purchase, the car depreciation calculator addresses the vehicle’s changing value rather than the loan.

The form’s calculation is specific: sales tax is calculated from the vehicle price, then added to the price, then the down payment is subtracted. The result is the financed principal. The calculator does not include a separate trade-in field, dealer documentation fees, registration, title fees, warranties, insurance, maintenance, fuel, or negative equity from an old loan. Add financed items to the vehicle price or down payment inputs only if that matches the contract you are modeling.

Inputs for a realistic car-payment estimate

Vehicle price is the negotiated price before sales tax in this calculator. If the dealer worksheet includes taxable add-ons, include them only when you want them financed. Down payment can represent cash down, a manufacturer rebate applied as down payment, or a net trade-in allowance. If you owe money on the traded vehicle, use the net amount after payoff, not the headline trade value.

Sales tax rate is applied to the full vehicle price. Actual tax rules differ by state and may treat trade-ins, rebates, and fees differently, so this is a simplified estimate. Interest rate is the annual rate used for monthly amortization. Loan term is entered in years and converted to months.

Formula

Sales tax is:

$\text{sales tax} = \text{vehicle price} \cdot \frac{\text{sales tax rate}}{100}$

The financed principal is:

$\text{principal} = \text{vehicle price} + \text{sales tax} - \text{down payment}$

The monthly rate and months are:

$\text{monthly rate} = \frac{\text{annual rate}}{100 \cdot 12}$

$\text{months} = \text{loan term years} \cdot 12$

For a positive rate:

$\text{monthly payment} = \frac{\text{principal} \cdot \text{monthly rate} \cdot (1 + \text{monthly rate})^{\text{months}}}{(1 + \text{monthly rate})^{\text{months}} - 1}$

For a zero-rate offer:

$\text{monthly payment} = \frac{\text{principal}}{\text{months}}$

Then:

$\text{total payment} = \text{monthly payment} \cdot \text{months}$

$\text{total interest} = \text{total payment} - \text{principal}$

$\text{total cost} = \text{total payment} + \text{down payment}$

Example

For a $30,000 vehicle, $5,000 down payment, 6.5% sales tax, 4.5% annual interest rate, and 5-year term, sales tax is $1,950. The total amount before down payment is $31,950, so the financed principal is $26,950. The monthly rate is 4.5 divided by 100 and divided by 12, or 0.00375. The term creates 60 payments.

The amortized payment formula returns a monthly payment of $502.43. Total payment over the loan is $30,145.76. Total interest is $3,195.76, and total cost including the $5,000 down payment is $35,145.76. Those figures match the form output for the defaults: sales tax $1,950, total cost $35,145.76, total interest $3,195.76, total payment $30,145.76, and 60 monthly payments.

APR, rebates, and dealer comparisons

Auto shoppers often compare a promotional APR with a cash rebate. A low APR can reduce interest, but a rebate can lower principal. The best choice depends on the price, term, rate, and whether the rebate is available with outside financing. Dealer add-ons can also change the true cost. A payment quoted in the showroom may exclude taxes, fees, or add-ons until the final contract, so compare itemized numbers.

A longer term can make a vehicle appear affordable while increasing total interest and negative-equity risk. If the car depreciates faster than the loan balance falls, selling or trading early can require bringing cash to closing. Compare the loan result with expected ownership costs in the budget calculator and with income capacity in the debt-to-income calculator.

Tips before signing

• Get at least one outside financing quote before visiting the dealer.
• Separate vehicle price negotiation from financing and trade-in discussions when possible.
• Check whether tax is calculated before or after trade-in credit in your state.
• Add financed fees and warranties to the vehicle price if they will be part of the loan.
• Consider insurance, maintenance, fuel, registration, and depreciation alongside the payment.

This calculator is informational and not financial advice. Actual auto loan terms depend on lender approval, state tax rules, dealer fees, vehicle price, and contract details.

Displayed results use the currency, time period, percentage, or other units named in the tool and round only for presentation; retain additional precision when carrying a result into another calculation.

Sources

• Consumer Financial Protection Bureau, Auto loans — consumer guidance on vehicle financing.
• Consumer Financial Protection Bureau, What is the difference between a loan interest rate and the APR? — APR and interest-rate comparison.
• Federal Trade Commission, Used Car Rule — federal consumer protection context for vehicle sales.
• Federal Reserve, Consumer Credit - G.19 — official consumer-credit data context.