Car Loan and Interest Calculator: Monthly Payment

A car loan and interest calculator estimates your fixed monthly payment and total interest from the amount borrowed, annual percentage rate (APR), and loan term. Enter those three figures to see the payment and interest estimate; it does not include vehicle taxes, insurance, fees, or other costs.

Formula

This calculator uses the standard fixed-payment loan formula. It treats APR as a nominal annual rate divided into monthly periods, and assumes one equal payment at the end of each month.

Monthly payment: M = P × r / [1 − (1 + r)⁻ⁿ]

Total interest: I = M × n − P

• P is the amount financed, in dollars.
• APR is the annual percentage rate, entered as a percentage, such as 8 for 8%.
• r is the monthly rate as a decimal: APR ÷ 1,200. At 8% APR, r = 0.08 ÷ 12.
• n is the number of monthly payments: loan term in years × 12.
• M is the monthly payment in dollars; the result is rounded to the nearest cent.
• I is the estimated total interest in dollars, calculated using the rounded monthly payment shown.

The payment formula spreads principal and interest across the full term. Early payments generally include a larger interest portion because interest is calculated on a higher outstanding balance; as principal is repaid, that portion declines. The formula assumes the same rate and scheduled payment throughout.

Worked Example

Using the calculator’s default inputs—$20,000 financed, 8% APR, and a five-year term—the number of payments is 5 × 12 = 60. The monthly rate is 8 ÷ 1,200 = 0.0066667.

Substitute those values into the payment formula:

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

Total interest is calculated from the displayed, rounded payment: $405.53 × 60 − $20,000 = $4,331.80. The estimated total of scheduled payments is therefore $24,331.80, before any costs not included in the inputs.

Assumptions

• The interest rate is fixed for the entire loan term.
• Payments are equal monthly payments made at the end of each month.
• Interest accrues monthly using APR divided by 12; this is a standard estimate and may differ from a lender’s exact calculation conventions.
• Fees, taxes, insurance, optional products, and other charges are not included. The calculator also does not model a down payment, trade-in, balloon payment, or extra payments unless those amounts are reflected in the loan amount or term.

What to Enter and How to Read the Results

Enter the amount actually financed rather than assuming it is the vehicle’s advertised price. The financed balance can differ from the price after a down payment, trade-in credit, or amounts added to the contract. Use the rate and term supplied in the lender’s written figures; a rate shown in an advertisement or a preliminary estimate may not be the rate in a final offer.

The monthly payment is the estimated scheduled installment for principal and interest alone. Total interest is the sum of those rounded installments minus the original loan amount. It is not the total cost of owning a car. Fuel, maintenance, registration, insurance, and costs associated with buying or selling the vehicle are outside this calculation.

For example, a longer term generally spreads repayment over more months and can reduce the amount due each month, but the balance is outstanding for longer. With a positive rate, that can increase total interest if the principal and rate are otherwise unchanged. This is a mathematical comparison, not a recommendation about which term to choose.

Choosing Inputs and Comparing Estimates

To compare two estimates meaningfully, keep the loan amount and APR consistent when examining the effect of different terms. To isolate the effect of a rate, keep the amount and term the same. If several inputs change at once, the payment difference cannot be attributed to one factor alone.

• Check whether the quoted amount is the cash price, the amount financed, or a payment estimate. The calculator needs the principal borrowed.
• Confirm whether a quoted rate is an APR or another rate measure. Do not enter a monthly rate in the APR field.
• Convert the term into years for this calculator. For instance, 48 months is 4 years.
• Use consistent figures from the same written estimate, including the same treatment of any amount added to the loan.
• Compare the displayed interest estimate with the lender’s payment schedule and disclosures, which may reflect additional details.

The calculator accepts APR values from 0.01% to 100% and terms from 0.0833 to 50 years as numerical input limits. Those ranges are not claims about available rates, loan offers, or typical terms; use the actual figures you have been given.

Common Calculation Problems and Limits

A frequent mistake is treating the vehicle price as the loan principal even when a down payment or trade-in changes the amount financed. Another is entering 8 when a rate is written as 0.08%—or entering 8% as 0.08 in a field that expects 8. Here the APR field expects percentage points: enter 8 for 8%.

Rounding also matters. The monthly payment is rounded to cents before total interest is calculated, so the total uses the displayed payment multiplied by the number of months. A lender’s final schedule can differ slightly because of payment dates, daily interest calculations, fees, rounding, or other contract details. A variable rate, irregular payments, skipped-payment arrangements, and additional principal payments are not represented by this fixed-payment model.

This result cannot establish whether a loan will be approved or whether the payment fits a particular budget. It also does not calculate a payoff quote, which can depend on the balance and timing of the payoff, or account for an early payment that changes the remaining schedule.

Frequently Asked Questions

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

Does the calculator include taxes and insurance?
No. It estimates principal and interest only. Enter an amount that matches the loan principal you want to model, and treat taxes, insurance, fees, and vehicle ownership costs separately.

Why is the total interest different from my lender’s figure?
The lender may use exact payment dates, daily accrual, contract-specific rounding, fees, or other details that this monthly estimate does not model. Compare the calculator’s assumptions with the lender’s payment schedule and disclosed figures.

Does a longer car loan term reduce interest?
Not necessarily. For the same principal and positive fixed rate, a longer term usually means more scheduled payments and can increase the total interest, even if the monthly installment is lower.

Can I use this calculator for a zero-interest loan?
The formula divides by the monthly rate, so the APR input starts at 0.01%. For a true 0% loan with equal payments, divide the amount financed by the number of monthly payments; confirm how the lender handles the contract.

Is the monthly payment the full cost of a car?
No. It is an estimate of the loan’s principal-and-interest payment. It excludes costs such as insurance, fuel, maintenance, and other charges.

The 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