Monthly Car Loan Calculator Payment and Total Interest

A monthly car loan calculator estimates your fixed monthly principal-and-interest payment from the amount financed, annual percentage rate (APR), and loan term. Enter those three figures to see the payment and the total interest implied by making that payment for the full term.

Formula

The calculator uses the standard fixed-payment loan formula. It converts the annual APR to a monthly rate, then calculates the level payment that amortizes the principal over the selected number of monthly payments.

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 calculated as the displayed monthly payment multiplied by the number of payments, minus the original principal: Total interest = monthly payment × n − P. The payment is rounded to cents before this total is calculated, so the estimate reflects repeated payments of that rounded amount.

Worked Example

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

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

Total interest = $405.53 × 60 − $20,000 = $4,331.80. The corresponding total of the scheduled payments is $24,331.80. Actual final payment amounts can differ slightly if a lender adjusts the schedule or rounds interest differently.

Assumptions

• The interest rate stays fixed for the entire loan term.
• Payments are made monthly, at the end of each monthly period.
• Interest is modelled monthly using APR ÷ 12.
• The calculation excludes fees, taxes, insurance, add-ons, and any other amount not included in the loan amount.

What to Enter and How to Read the Result

Loan amount means the amount borrowed, not necessarily the vehicle’s advertised price. A down payment or trade-in credit may reduce the amount financed, while taxes, registration costs, optional products, or rolled-in balances may increase it. Use the amount shown in the lender’s financing paperwork or a carefully calculated estimate; do not enter a vehicle price if the amount borrowed will be different.

APR is an annualized rate expressed as a percentage. Enter 8 for 8%, not 0.08. The calculator converts the entered percentage to a monthly decimal rate. A lender’s quoted APR and the rate used to calculate a payment can be affected by how the loan is structured; use the figure supplied for the specific financing offer and check its disclosure for the exact calculation.

Loan term is entered in years. The formula multiplies it by 12, so five years means 60 monthly payments. The displayed payment covers principal and interest only. It is not a complete estimate of vehicle ownership costs or the full amount due each month if other charges are collected alongside the loan payment.

How Loan Amount, APR, and Term Affect the Payment

• A larger amount financed increases the payment when rate and term are unchanged. It also generally increases the total interest because interest accrues on a larger principal balance.
• A higher APR raises the payment and the interest cost for the same amount and term. The exact change depends on all three inputs.
• A longer term usually lowers the scheduled monthly payment by spreading repayment across more months, but it can increase total interest because the balance remains outstanding for longer.

These are mathematical relationships, not a recommendation about which loan structure to choose. To compare two estimates on equal terms, enter each amount, APR, and term separately and consider both the monthly payment and total interest. A lower payment by itself does not show that the overall borrowing cost is lower.

Common Misunderstandings and Limits

A frequent mistake is treating the calculator’s payment as the entire monthly cost of owning a car. The formula includes only scheduled principal and interest. Insurance, fuel, maintenance, parking, and other costs are outside the calculation; taxes or other charges may also be excluded unless they are financed in the amount entered.

Another common error is entering the car’s price instead of the amount financed, or entering 0.08 when the APR field expects 8 for eight percent. Confirm the units before calculating. Results are rounded to cents, and lenders may use specific payment dates, daily interest accrual, fees, or rounding procedures that produce small differences from this standard monthly model.

The formula assumes equal payments and a fixed rate. It does not model a variable rate, a balloon or final lump-sum payment, skipped or late payments, extra principal payments, or refinancing. It also does not determine a lender’s charges, terms, or approval decision. Obtain actual figures from the lender and review the loan disclosure for details that are not represented by these inputs.

Frequently Asked Questions

How do I calculate a monthly car loan payment?
Convert APR to a monthly decimal by dividing by 1,200, and convert the term to months by multiplying years by 12. Apply the fixed-payment formula shown above to the amount financed, monthly rate, and number of payments.

Does the monthly payment include insurance and taxes?
No. This estimate covers principal and interest only. It excludes insurance and other costs unless a charge is included in the loan amount, in which case it affects the amount financed.

Why can my lender’s payment differ from the calculator?
The lender may use different rounding, payment dates, fee treatment, or interest-accrual details. Check that the amount financed, APR, and term match the lender’s figures, then consult the disclosure for the scheduled payment and any included charges.

Does a longer car loan term reduce total interest?
A longer term generally spreads the principal over more payments and may reduce the monthly payment, but it can increase total interest because repayment takes longer. The calculator shows both the payment and estimated interest for the inputs entered.

What is the difference between APR and the monthly interest rate?
APR is entered as a yearly percentage. This calculator divides it by 12 to get a monthly rate and by 100 to express that rate as a decimal. For example, 8% APR becomes 0.0066667 per month in the formula.

This result is an estimate; 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