APR Calculator for Car Loans With a Down Payment

This APR calculator estimates a car loan’s monthly payment and total interest after a down payment, using the amount borrowed, APR, and loan term. Enter the vehicle’s price less your down payment as the loan amount; the results show the scheduled payment and interest, not taxes or lender fees.

Formula

The calculator uses the standard fixed-payment loan formula. Monthly payment = P × r ÷ [1 − (1 + r)⁻ⁿ], where r = APR ÷ 1,200 and n = years × 12. Total interest = (monthly payment × n) − P.

• P is the amount financed, in dollars: generally the vehicle price plus amounts added to the loan, minus the down payment and any trade-in credit applied.
• APR is the annual percentage rate entered as a percentage, such as 8 for 8%.
• r is the monthly rate as a decimal.
• n is the number of monthly payments.

The calculator rounds the monthly payment to cents. Its total-interest result uses that rounded payment multiplied by the number of scheduled months, then subtracts the original principal. A lender’s final payment may differ slightly because of its payment schedule, rounding, or payoff adjustments.

Worked Example

Using the calculator’s defaults—$20,000 financed, 8% APR, and five years—the term is 5 × 12 = 60 monthly payments. The monthly rate is 8 ÷ 1,200 = 0.0066667.

Monthly payment = 20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰] = $405.53, rounded to the nearest cent.

Total interest = ($405.53 × 60) − $20,000 = $4,331.80. The scheduled payments total $24,331.80, of which $20,000 repays principal and $4,331.80 is estimated interest.

Assumptions

• The APR stays fixed throughout the loan.
• There is one payment each month, with payments made at the end of each monthly period.
• Interest compounds monthly at APR divided by 12.
• The estimate excludes fees, taxes, insurance, optional products, and other costs unless they are included in the amount financed.

How a Down Payment Changes the Estimate

A down payment reduces the amount that must be financed; it is not a separate subtraction from the calculator’s payment after the loan amount is entered. For a simple estimate, start with the vehicle price, add any charges that will be financed, then subtract the down payment and trade-in value that will be credited toward the purchase. Enter the resulting amount as P.

For example, if a vehicle costs $25,000 and a buyer puts $5,000 down, the basic amount financed is $20,000 before any taxes, fees, trade-in, or other financed items. At the same APR and term, a smaller principal produces a smaller scheduled payment and less total interest. The exact difference depends on the rate and term because interest accrues on the outstanding balance.

A down payment does not change the APR by itself in this formula. APR is a separate input; use the figure provided in the lender’s loan disclosure. The calculator cannot determine an APR from a down payment or vehicle price.

What APR and the Results Mean

APR is a yearly rate expressed as a percentage and is intended to represent borrowing cost on an annualized basis. This calculator uses APR as a nominal annual rate divided into 12 monthly periods. It does not independently calculate an APR from fees. If a lender’s disclosed APR includes costs not represented in the simple monthly-interest formula, the calculator’s estimate may not match the lender’s full disclosure.

The monthly payment is the scheduled principal-and-interest amount under the stated assumptions. Total interest is the estimated interest over all scheduled payments, not the full cost of owning the car. Fuel, maintenance, registration, insurance, and other ownership expenses are outside this calculation.

Comparing scenarios can show how changing one input affects payment arithmetic. Keep the other inputs unchanged when examining the effect of a different down payment, APR, or term. A longer term spreads repayment across more months and can reduce the scheduled payment, while the total interest may rise because the balance remains outstanding for longer.

Common Inputs and Calculator Limits

Use the amount actually financed rather than automatically entering the advertised vehicle price. If taxes or fees are paid separately, do not add them to P; if they are rolled into the loan, include them. Likewise, subtract a down payment only once. Entering a price that already reflects the down payment and subtracting it again understates the loan.

• Use APR as a percent: enter 8 for 8%, not 0.08. The formula converts it to a monthly decimal.
• Use years for the term: five means 60 monthly payments, not five payments.
• Check the financed total: add only costs actually included in the loan and subtract applicable upfront contributions once.
• Expect rounding: a lender may adjust the final payment or calculate accrued interest using specific dates, so small differences are possible.

This is a level-payment estimate, not a complete loan contract model. It does not account for variable rates, irregular payment dates, skipped payments, extra principal payments, late charges, prepayment terms, or changes in the amount owed. If the loan has unusual terms, use the lender’s payment schedule for exact figures.

Frequently Asked Questions

Does a down payment lower the APR on a car loan?
A down payment lowers the amount financed in this calculator, not the APR. Enter the APR quoted in the lender’s disclosure as a separate input.

Should I enter the car price or the amount after my down payment?
Enter the amount financed after subtracting the down payment and any trade-in credit, and after adding costs that will be included in the loan.

Does this calculator include taxes and fees?
No. Add taxes or fees to the loan amount only if they are being financed. Costs paid separately are not part of the payment estimate.

Why might my lender’s payment differ?
The contract may use different rounding, payment dates, financed charges, or terms. The calculator also assumes a fixed rate and regular monthly payments.

Does a longer car loan term reduce total interest?
Not necessarily. A longer term can lower the scheduled monthly payment, but it generally means interest is calculated over more payment periods under the same rate and principal assumptions.

This result is an estimate for educational purposes; the lender’s disclosure gives the exact figures.

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in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2