New Car Payment Calculator: Estimate Monthly Costs

This new car payment calculator estimates the fixed monthly principal-and-interest payment from the amount borrowed, APR, and loan term. Enter those three figures to see the estimated monthly payment and total interest; taxes, fees, insurance, and other ownership costs are not included.

Formula

The calculator uses the standard fixed-payment loan formula. It first converts the annual percentage rate (APR) into a monthly rate, calculates the level monthly payment over the full term, and rounds that payment to the nearest cent:

Monthly payment = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]

• P is the amount financed, in dollars. This is the loan principal, not necessarily the car’s advertised price.
• r is the monthly interest rate as a decimal: APR ÷ 1,200. For an 8% APR, r = 8 ÷ 1,200.
• n is the number of monthly payments: loan term in years × 12.
• round(…, 2) rounds the payment to two decimal places, or cents.

Total interest is estimated as rounded monthly payment × number of payments − principal. Because this calculation uses the rounded payment for every installment, the displayed total reflects that convention. A lender’s final schedule may differ slightly because of payment dates, daily interest, or other contract details.

Worked Example

Using the calculator’s default inputs—$20,000 borrowed, 8% APR, and a five-year term:

1. Convert APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 months.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = approximately $405.53 per month after rounding.
4. Calculate interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The estimated monthly payment is $405.53, and estimated total interest is $4,331.80. These are formula outputs, not a quote or a statement about any particular loan offer.

Assumptions

• The interest rate stays fixed for the full repayment term.
• Payments are equal monthly installments, with the standard amortization assumption that the first payment is made one month after borrowing.
• Interest is modelled monthly using APR divided by 12; the formula does not model daily accrual or irregular payment dates.
• The loan is fully repaid through the scheduled payments, with no missed, extra, or late payments.
• The estimate excludes taxes, title and registration costs, dealer or lender fees, insurance, optional products, and other charges unless they are included in the amount borrowed.

What Amount Should You Enter?

Enter the amount financed, rather than automatically entering the vehicle’s sticker price. A simplified way to estimate it is:

Amount financed ≈ negotiated vehicle price + items financed − down payment − trade-in credit

For example, if a vehicle price is $28,000, the amount financed will not necessarily be $28,000. A down payment or trade-in may reduce the balance, while taxes, fees, or optional items added to the loan may increase it. The figures depend on the actual transaction. Use the amount shown in the lender’s loan disclosure when available; do not subtract a trade-in balance or add costs twice.

A vehicle’s purchase price and its loan principal are different quantities. If a trade-in has an outstanding loan balance, that balance can affect the amount financed, but the calculator cannot determine the transaction’s treatment without the relevant figures.

How to Read the Estimate

The monthly payment is the scheduled amount for principal and interest under the inputs. Early in an amortizing loan, a larger share of each payment generally goes toward interest; later, more goes toward reducing principal. The total-interest result is the estimated interest across all scheduled payments, not the total cost of owning or operating the car.

To see how the assumptions affect the estimate, change one input at a time. A larger principal raises the payment when the rate and term stay fixed. A higher APR also raises the payment. A longer term usually lowers the scheduled monthly amount, but leaves the balance outstanding for more months and can increase total interest. The exact change depends on all three inputs.

Compare loan offers using the same principal, APR, and term, and check the lender’s disclosure for the payment schedule and total amount due. APR is an annualized borrowing-cost measure, but a calculator that treats it as a monthly rate does not reproduce every fee or payment-timing convention in a contract. Use the actual rate and financed amount supplied for the offer you are examining.

Common Mistakes and Limits

• Using the sale price as the loan amount: The down payment, trade-in, and financed add-ons can change the principal.
• Entering 8 instead of 0.08: Enter APR as a percentage, such as 8 for 8%, not as a decimal. The calculator converts it to a monthly decimal rate.
• Mixing years and months: The term field is in years. A five-year term means 60 monthly payments.
• Assuming the result includes all vehicle costs: Fuel, maintenance, insurance, and other ownership expenses are outside this loan formula.
• Expecting an exact contract quote: Payment dates, lender rounding, fees, and other contract terms can change the actual schedule.

The formula is intended for a fixed-rate loan repaid in equal monthly installments. It is not designed for a variable rate, balloon payment, lease, changing payment schedule, or a loan with additional charges that are not included in the principal. The APR input must be greater than zero for this version of the formula.

Frequently Asked Questions

How do I calculate a new car payment?
Use the amount financed, APR, and term in months. Convert APR to a monthly rate by dividing by 1,200, then apply the fixed-payment formula shown above. This calculator performs those steps and rounds the monthly result to cents.

Does the estimated payment include sales tax and insurance?
No. It estimates principal and interest only. If a cost is added to the amount borrowed, include it in the principal; insurance and costs paid separately are not part of the result.

Does choosing a longer term reduce the total cost?
A longer term generally spreads repayment across more installments and can lower the monthly payment, but it can increase total interest because interest accrues over more months. The calculator displays both payment and estimated interest for the inputs entered.

Should I enter the car price or the amount financed?
Enter the amount financed. It may differ from the vehicle price because of a down payment, trade-in, financed fees, or other items. Check the lender’s paperwork for the actual principal.

Why might a lender’s payment differ from this estimate?
The contract may use different payment dates, rounding, fees, or interest-accrual details. The calculator also excludes costs not included in the principal and assumes fixed monthly installments.

This result is an estimate; 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 | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2