Auto Loan Monthly Payment Calculator and Formula

This auto loan calculator estimates your fixed monthly principal-and-interest payment from the amount financed, APR, and loan term. Enter those three figures to see the monthly payment and total interest calculated using a standard fixed-rate loan formula.

Formula

The calculator uses the standard level-payment formula for a fixed-rate loan that is repaid in equal monthly installments:

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

• P is the amount borrowed or financed, in dollars.
• r is the monthly interest rate, calculated as APR ÷ 1,200. APR is entered as a percentage per year; for example, 8% gives a monthly rate of 0.08 ÷ 12.
• n is the number of monthly payments, calculated as loan term in years × 12.

The result is rounded to the nearest cent. Total interest is calculated as the rounded monthly payment multiplied by the number of payments, minus the original loan amount. This total assumes every scheduled payment is made and does not include charges outside the loan balance.

Worked Example

Using the calculator’s defaults—$20,000 financed, 8% APR, and a five-year term—the calculation is:

1. Convert APR to a monthly decimal rate: 8 ÷ 1,200 = 0.0066667.
2. Find the number of monthly payments: 5 × 12 = 60.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
4. The monthly payment, rounded to cents, is $405.53.
5. Total interest using the rounded payment is $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The interest rate remains fixed for the entire term.
• Payments are equal, made monthly, with the first payment one month after the loan begins.
• Interest is treated as compounding monthly at APR divided by 12.
• The calculation excludes fees, taxes, insurance, optional products, and any other costs not included in the amount financed.

What the Monthly Payment Includes

This estimate is the scheduled principal-and-interest payment: part of each payment covers interest accrued on the remaining balance, and the rest reduces principal. At the start of a fully amortizing loan, the balance is larger, so more of the payment generally goes toward interest. As the balance declines, the interest portion declines and more of each equal payment reduces principal.

A vehicle’s total ownership or purchase cost can differ from this loan payment. Taxes, registration, insurance, maintenance, and fees may affect the amount paid overall, but they are not included unless they are added to the financed amount. A quote may also show an amount due at signing or a separate recurring charge; those are not represented by this formula.

Using the Estimate and Checking Inputs

For a useful estimate, enter the amount actually being financed rather than assuming it equals the vehicle’s advertised price. The financed amount can reflect a down payment, trade-in credit, or items rolled into the loan, depending on the transaction. Use the APR and term shown in the lender’s disclosure or quote, rather than relying on a general rate assumption.

• Check that APR is entered as a percentage, such as 8 for 8%, not as 0.08.
• Enter the term in years. A 60-month term is 5 years.
• Use the loan principal after any down payment or other adjustments if those amounts change what is borrowed.
• Compare the displayed payment and interest total with the lender’s itemized figures, which may include additional amounts or different payment timing.

The calculator’s APR input begins at 0.01% because the displayed formula divides by the monthly rate. A zero-interest loan is a separate simple case: its principal-only payment is the amount financed divided by the number of payments. For example, $20,000 over 60 payments with no interest would be $333.33 per month, before any other charges.

Limits and Common Misunderstandings

A calculated payment is not a lender’s offer, approval decision, or complete measure of the cost of borrowing. The APR, amount financed, and term are inputs; the calculator cannot verify them. Obtain the actual figures from the lender, and check whether a quoted payment includes only principal and interest or also includes other amounts.

Rounding can create small differences from a lender’s schedule. This tool rounds the regular payment to cents and uses that rounded figure for its total-interest estimate. A lender may calculate interest according to its contract and payment dates, and the final payment can be adjusted to clear a small remaining balance. Extra payments, late payments, a variable rate, or a changed payment schedule also make the simple estimate less applicable. The formula assumes equal monthly payments and a fixed rate throughout the term.

Another frequent misunderstanding is that a lower monthly payment necessarily means less interest overall. A longer term gives more months for payments to be made, so the total interest calculation can rise even when the monthly amount falls. The payment figure alone does not show all costs or determine whether a particular loan fits a person’s circumstances.

Frequently Asked Questions

How do I calculate an auto loan payment by hand?
Convert APR to a monthly decimal rate by dividing the percentage by 1,200, then use the level-payment formula with the loan principal and total number of monthly payments. For a five-year term, the payment count is 60.

Does an auto loan payment calculator include insurance and taxes?
Not in this calculator. It estimates principal and interest only. Costs such as insurance or taxes are excluded unless they have been added to the amount financed, and they may be billed separately.

Why is my lender’s payment different from this estimate?
The loan amount, APR, term, fees, payment dates, or rounding method may differ. Check the lender’s itemized disclosure and confirm that you entered the same principal, APR, and term used in the quote.

Does a longer auto loan term lower the monthly payment?
For the same principal and APR, spreading repayment over more months generally lowers the scheduled payment, while increasing the number of payments. The total interest depends on the inputs and the payment calculation; the calculator shows its estimate.

What if my auto loan has a 0% interest rate?
This calculator requires a positive APR. For a true zero-interest loan with equal payments, divide the financed amount by the number of monthly payments; other charges may still apply.

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

Related

• Loan Calculator With Variable Payments: How It Works
• Loan Calculator With Payment Amount and Total Interest
• Monthly Loan Repayment Calculator and Payment Formula

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