New Car Loan Repayment Calculator and Payment Formula

This new car loan repayment calculator estimates a fixed monthly payment and total interest from the amount financed, annual percentage rate (APR), and loan term. Enter those figures to see the payment and the interest implied by the calculator’s assumptions.

Formula

The calculator uses the standard fixed-payment loan formula, with the monthly payment rounded to the nearest cent:

Monthly payment = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the amount financed, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1,200. For an 8% APR, r = 0.08 ÷ 12.
• n is the number of monthly payments: loan term in years × 12.
• Total interest is the rounded monthly payment × number of payments − amount financed, in dollars.

The formula assumes a positive fixed APR and equal monthly payments. The calculator’s first result is the estimated monthly payment; total interest is a separate estimate calculated using that payment rounded to cents.

Worked Example

Using the calculator’s default inputs—$20,000 financed, 8% APR, and five years—the term is 5 × 12 = 60 monthly payments. The monthly rate is 0.08 ÷ 12 = 0.0066667.

Substitute the figures into the payment formula:

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

Total of the rounded payments: $405.53 × 60 = $24,331.80. Estimated interest: $24,331.80 − $20,000 = $4,331.80.

Assumptions

• The interest rate stays fixed for the full loan term.
• Payments are monthly, made at the end of each payment period, with the first payment one month after the loan begins.
• Interest is compounded monthly using APR divided by 12.
• The calculation does not include fees, taxes, insurance, optional products, or other amounts unless they are already part of the amount financed. It does not model payment-date changes or a changing balance from extra payments.

What the Calculator Tells You

The monthly payment is the scheduled principal-and-interest amount under the stated assumptions. Total interest is the estimated interest across all scheduled payments. Together, the outputs help translate a quoted amount financed, APR, and term into two comparable figures. They are calculations, not a loan offer or a complete estimate of vehicle ownership costs.

For a new-car quote, the amount financed is not necessarily the vehicle’s advertised price. It may reflect the transaction amount after any down payment or trade-in credit, plus any charges or optional items included in the financing. To model a quote, use the amount the lender says will actually be financed, rather than automatically entering the sticker price. Get the actual amount, APR, and term from the lender; the default APR is only an example input and is not a current-rate claim.

The result also does not show a full amortization schedule. In a standard amortizing loan, each payment covers the interest accrued for that period and reduces principal by the remainder. Early payments generally contain a larger interest portion than later payments when the rate and payment remain fixed. The calculator’s total-interest figure summarizes the schedule rather than showing each installment’s breakdown.

How to Use the Estimate Carefully

1. Enter the amount financed in dollars. Use the loan amount, not a monthly budget or the vehicle’s price before adjustments.
2. Enter the annual APR as a percentage, such as 8 for 8%, not 0.08. The tool converts it to a monthly decimal rate.
3. Enter the term in years. A term with a fraction of a year is converted to months by multiplying by 12.
4. Read the monthly payment and total interest, then check that the inputs match the figures in the written quote.

Loan comparisons require consistent inputs. If one calculation uses a different financed amount or term, its payment and total interest cannot be attributed to APR alone. Likewise, a lower monthly payment can result from a longer term rather than a lower overall borrowing cost. Review the amount financed, payment count, and any charges alongside the payment estimate.

Common Limits and Misconceptions

A frequent misunderstanding is that the monthly payment is the complete cost of a new car. It covers only the modeled loan repayment. Insurance, fuel or charging, maintenance, registration, and other ownership expenses are outside this formula. Taxes and fees are also not separately calculated; they affect the result only if included in the amount financed entered.

Rounding matters. The monthly payment is rounded to cents before total interest is calculated, so multiplying an unrounded payment by the term may produce a slightly different total. A lender’s final payment schedule can also differ because of its precise payment dates, rounding method, fees, or contract terms.

The calculator is not suitable as-is for a variable-rate loan, irregular payments, a balloon payment, or a loan with a separate final balance. It does not account for extra principal payments, skipped or late payments, or a payoff before the scheduled end. Those cases need additional inputs and a different calculation.

Frequently Asked Questions

How do I calculate a new car loan payment?
Use the amount financed, monthly interest rate (APR divided by 1,200), and number of monthly payments in the fixed-payment formula shown above. This calculator performs that calculation and rounds the payment to cents.

Should I enter the car’s price or the amount financed?
Enter the amount financed shown for the loan. It may differ from the car’s price because of a down payment, trade-in credit, or charges included in the loan.

Does the calculator include taxes and insurance?
No. It estimates principal and interest only. Taxes, insurance, and other costs are not included unless an amount is incorporated into the loan balance you enter.

Why can a longer loan term lower the monthly payment?
A longer term spreads repayment over more monthly installments. With the same amount and APR, that usually changes both the payment size and the number of periods over which interest accrues; the calculator reflects that arithmetic.

Why does my lender’s payment differ from this estimate?
The contract may use different inputs or include fees, a different payment schedule, or other terms not represented here. Check the amount financed, APR, term, and disclosed payment schedule against your entries.

This result is an estimate, and the lender’s disclosure gives the exact figures.

Related

• Car Loan Calculator With Down Payment: Monthly Car Payment
• Auto Loan Calculator With Trade-In and Amount Owed (Negative Equity)

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