New Car Loan APR Calculator and Payment Formula

This new car loan APR calculator estimates the monthly payment and total interest for a fixed-rate loan using the amount borrowed, APR, and term. Enter the figures from a lender’s offer to see the estimated cost; the calculation does not look up or predict available APRs.

Formula

The calculator treats the APR as a nominal annual rate divided into monthly periods. It first calculates a level monthly payment, rounds that payment to cents, then estimates total interest as all rounded payments minus the amount borrowed.

• p = amount borrowed, in dollars.
• apr = annual percentage rate entered as a percentage, such as 8 for 8% per year.
• r = monthly rate, calculated as apr ÷ 1,200.
• n = number of monthly payments, calculated as years × 12.
• pmt = monthly payment in dollars: round[p × r ÷ (1 − (1 + r)⁻ⁿ), 2].
• Total interest = pmt × n − p, in dollars.

The payment formula spreads repayment across equal monthly installments. Each payment covers interest accrued for the period and reduces principal. Early in the schedule, the interest share is generally larger because the outstanding balance is larger; as principal is repaid, the interest portion declines.

Worked Example

Using the calculator’s default inputs—$20,000 borrowed, 8% APR, and five years—the number of payments is 5 × 12 = 60. The monthly rate is 8 ÷ 1,200 = 0.0066667, or about 0.66667% per month.

1. Substitute the values: payment = $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
2. Calculate the unrounded payment, about $405.53, then round to the nearest cent: $405.53 per month.
3. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

These figures are estimates under the formula’s assumptions. Actual payment schedules can differ because a lender may use different timing, rounding, or contract terms.

Assumptions

• The APR stays fixed for the full loan term.
• Payments are equal, made monthly, and begin one month after the loan starts.
• Interest accrues monthly at APR ÷ 12, represented as apr ÷ 1,200 when APR is entered as a percentage.
• The estimate excludes fees, taxes, insurance, add-ons, down payment, trade-in value, and any separate charges unless reflected in the amount borrowed or APR you enter.

What a New-Car Loan APR Means

APR is an annualized measure of borrowing cost expressed as a percentage. It can reflect the interest rate and, depending on the loan and disclosure method, certain finance charges. It is not the same thing as the monthly rate used in the payment formula: for this calculator, the monthly rate is APR divided by 12, then expressed as a decimal.

A quoted APR alone does not reveal the full amount you will pay. The principal, repayment term, fees included in the transaction, and payment schedule all matter. Two loans with the same APR can have different monthly payments if their amounts or terms differ. A longer term generally spreads repayment over more months, reducing the scheduled payment in many cases while increasing the number of periods over which interest accrues.

For an accurate estimate, use the amount actually financed rather than the vehicle’s advertised price. The financed amount may be affected by a down payment, trade-in credit, taxes, fees, or optional products. Check the lender’s written offer for the APR, term, payment amount, total of payments, and any charges; enter the relevant amount and rate into the calculator.

How to Use and Read the Estimate

• Loan amount: Enter the amount borrowed, not an assumed vehicle price. Use the lender’s stated amount financed when available.
• APR: Enter the annual percentage as a number. For example, type 8 for 8%, not 0.08.
• Term: Enter years, including a fraction where needed. The calculator converts years to months; a term of 5 years means 60 payments.
• Monthly payment: This is the estimated level payment before any items the formula does not model.
• Total interest: This is estimated interest over the full schedule using the rounded monthly payment. It is not the total amount paid; add the borrowed principal to get that amount.

For example, the default result means 60 payments of $405.53, or $24,331.80 in total payments. Of that amount, $20,000 repays principal and $4,331.80 is estimated interest. Because payments are rounded to cents, the final payment on an actual schedule can be adjusted slightly to clear the remaining balance.

Comparing Offers and Common Mistakes

When comparing written offers, keep the financed amount and repayment period consistent if you want to isolate how the APR affects the estimate. Then review the lender’s disclosed total payments and charges as well as its monthly figure. A payment can look lower simply because the term is longer; that does not by itself show the overall borrowing cost.

• Do not confuse APR with the monthly rate. Dividing APR by 12 gives a monthly percentage; divide by 100 as well to express it as a decimal.
• Do not enter 8% as 0.08. The calculator expects 8.
• Do not treat the vehicle price as the loan amount if the amount financed is different.
• Do not assume a payment estimate includes insurance, registration costs, maintenance, or optional products.
• Do not compare monthly payments without checking loan term and total payments.

APR and fees are specific to an offer and borrower, and this calculator cannot determine them. Obtain the actual figures from the lender’s disclosures rather than relying on an assumed or advertised rate.

Limits and Other Costs

This is a standard fixed-rate, fully amortizing loan calculation. It does not model a variable rate, irregular payment dates, a balloon payment, skipped or late payments, extra principal payments, refinancing, or a changing balance caused by additional charges. The result also does not determine whether an application will be approved or what rate may be offered.

To estimate a particular offer, use the disclosed amount financed, APR, and number of scheduled monthly payments. If the lender’s payment differs, check whether its amount includes charges or uses a different schedule. The lender’s contract and disclosure—not this arithmetic—set the exact terms. This result is an estimate, and the lender’s disclosure gives the exact figures.

Frequently Asked Questions

What is a new car loan APR?
It is an annualized percentage measure of the cost of borrowing for a new-car loan. The lender’s disclosure explains the APR and which finance charges are reflected in it.

How do I calculate a monthly car payment from APR?
Convert APR to a monthly decimal rate by dividing the percentage by 1,200, convert the term to months, then use the fixed-payment formula shown above. This calculator performs those steps and rounds the payment to cents.

Is APR the same as the interest rate?
Not necessarily. The interest rate measures the cost of borrowing principal, while APR is an annualized measure that may also account for certain finance charges. Check the offer’s definitions and disclosures.

Does a longer car loan term lower the monthly payment?
For the same amount and APR, spreading repayment across more months generally lowers the scheduled payment, but interest accrues across more payment periods. Compare the term and total payments, not just the monthly amount.

Does this estimate include taxes and insurance?
No. The formula excludes taxes, insurance, and other costs unless an amount is included in the loan amount or otherwise reflected in the APR. Use lender disclosures for the actual payment and charges.

Related

• Loan Application vs Down Payment Assistance: Key Differences
• Loan Application Letter: What to Include and How It Works
• Loan Application Online? Estimate Monthly Payments

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 | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2