Auto Loan Calculator Monthly Payment and Total Interest

An auto loan calculator estimates your fixed monthly payment and total interest from the amount borrowed, annual percentage rate (APR), and loan term. Enter those figures to see the scheduled payment and the interest paid over the full term; the estimate excludes costs that are not included in the loan amount.

Formula

The calculator uses the standard fixed-payment loan formula. It divides the loan principal into equal monthly payments that cover interest due each month and repay the balance by the end of the term:

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

Total interest = (monthly payment × n) − P

• P is the amount borrowed, in dollars.
• r is the monthly interest rate, calculated as APR ÷ 1,200. For an APR of 8%, r = 0.08 ÷ 12.
• n is the number of monthly payments: loan term in years × 12.
• APR is the annual percentage rate entered as a percentage, not a decimal. The calculator’s interest calculation treats APR as the annual rate divided into monthly periods.

The calculator displays the payment to the nearest cent. Total interest is calculated using that displayed, rounded payment multiplied by the number of months, then subtracting the principal. An actual lender’s schedule may differ slightly because of payment dates, rounding practices, fees, or the contract’s interest calculation method.

Worked Example

Using the defaults—$20,000 borrowed, 8% APR, and a five-year term—the loan has 60 monthly payments. The monthly rate is 0.08 ÷ 12 = 0.0066667.

1. Calculate the payment: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
2. The result is approximately $405.53 per month, rounded to the nearest cent.
3. Calculate the total of scheduled payments: $405.53 × 60 = $24,331.80.
4. Subtract the principal: $24,331.80 − $20,000 = $4,331.80 in estimated total interest.

The actual payment can vary if a lender uses different conventions or adds financed charges to the principal. This example is a mathematical estimate, not a lender quote.

Assumptions

• The interest rate is fixed for the full loan term.
• Payments are equal, made monthly, and begin on the assumed schedule; the formula does not model the exact calendar date of a payment.
• Interest is modelled monthly at APR ÷ 12.
• Taxes, title or registration costs, insurance, service contracts, lender fees, and other charges are not included unless they are already part of the amount borrowed. The calculator does not model late payments, skipped payments, or extra principal payments.

How to Use the Auto Payment Estimate

Use the amount you expect to finance—not automatically the vehicle’s advertised price. A down payment or trade-in value can reduce the amount financed, while any charges rolled into the loan can increase it. For a realistic estimate, use the amount and APR supplied by the lender and the term being considered. If you do not yet have a lender’s APR, treat any number you enter as a scenario rather than a prediction of the rate you will receive.

• Loan amount: Enter the principal after applying any down payment or trade-in credit and adding any costs that will be financed.
• APR: Enter the annual percentage rate as a percent, such as 8 for 8%, rather than 0.08. Ask the lender which rate figure to use if the offer distinguishes APR from another quoted interest rate.
• Term: Enter the number of years. The formula converts years to monthly payments; a term can also be expressed in months by dividing by 12.

The monthly payment is the scheduled installment for principal and interest under these assumptions. It is not necessarily the whole monthly cost of owning or operating a vehicle. Insurance, fuel, maintenance, parking, and other expenses are outside the calculation.

What Changes the Payment and Total Interest?

For the same principal and APR, a longer term generally lowers the required monthly installment because repayment is spread over more months. It also generally increases the total interest, since interest accrues over a longer period. A higher principal or APR raises the calculated payment when the other inputs stay unchanged. These are formula relationships, not a judgment about which loan is suitable.

To compare two estimates meaningfully, keep the assumed amount financed consistent and examine both the monthly payment and total interest. A lower payment alone does not show the full cost: it could reflect a longer term, a lower principal, a different APR, or some combination. If an offer includes a balloon payment, variable rate, or irregular payment schedule, this standard fixed-payment calculator does not represent it accurately.

Common Mistakes and Limits

• Using the vehicle price instead of the financed amount: The amount borrowed may differ after a down payment, trade-in, and financed charges.
• Entering APR in the wrong format: Enter 8 for 8%, not 0.08. The formula divides the entered percentage by 1,200 to get a monthly rate.
• Reading total interest as total paid: Total interest excludes repayment of principal. In the example, total scheduled payments are $24,331.80; $4,331.80 of that is estimated interest.
• Assuming the result includes every vehicle cost: The result covers only modeled loan payments and does not include insurance, operating costs, or unfinanced charges.
• Expecting exact statement figures: Payment dates, daily-interest methods, fees, and cent-rounding can cause a lender’s disclosure or amortization schedule to differ.

The formula assumes a fixed rate and equal payments that fully amortize the balance. It is not designed for a variable rate, deferred interest, a balloon balance, an irregular first period, or a loan with extra payments. For the contract’s exact payment schedule and charges, use the lender’s written figures.

Frequently Asked Questions

How do I calculate a monthly auto loan payment?
Use the principal, monthly rate (APR divided by 1,200), and number of monthly payments in the fixed-payment formula. The calculator applies that formula and rounds the monthly result to cents.

Does an auto loan payment include insurance?
No. This estimate includes only the loan payment calculated from principal, APR, and term. Insurance and other vehicle expenses are not part of the formula.

Why does a longer car loan term lower the monthly payment?
A longer term spreads repayment across more monthly installments. With the same principal and APR, it generally increases the total interest because interest is charged over more time.

Is APR the same as the monthly interest rate?
No. APR is entered as a yearly percentage. This calculator converts it to a monthly rate by dividing by 12 and by 100, or APR ÷ 1,200.

Why is my lender’s payment different from the calculator?
The loan amount, APR, payment dates, included charges, rate conventions, and rounding may differ. Check the lender’s disclosure for the contract-specific payment and total cost.

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