Monthly Car Payment Calculator: Estimate Your Auto Loan

A monthly car payment calculator estimates the regular payment on a fixed-rate auto loan from the amount borrowed, annual percentage rate (APR), and term. Enter those three figures to see the monthly payment and the total interest implied by the estimate.

Formula

The calculator uses the standard fixed-payment amortizing loan formula. It converts the annual APR to a monthly rate, calculates the payment needed to repay principal and interest over the term, then rounds the payment to cents.

• Monthly payment: M = round(P × r / [1 − (1 + r)⁻ⁿ], 2)
• Total interest: I = M × n − P
• Monthly rate: r = APR / 1200
• Number of payments: n = years × 12

P is the loan principal in dollars, APR is the annual percentage rate entered as a percentage, r is the monthly rate as a decimal, n is the number of monthly payments, M is the rounded monthly payment in dollars, and I is the estimated total interest in dollars. The APR input must be above zero because the displayed payment formula divides by the monthly rate.

Worked Example

Using the calculator’s default inputs—$20,000 borrowed, 8% APR, and five years—the number of payments is 5 × 12 = 60. The monthly rate is 8 / 1200 = 0.0066667.

1. Calculate the growth factor: (1 + 0.0066667)⁶⁰ ≈ 1.4898.
2. Calculate the payment: $20,000 × 0.0066667 / [1 − (1.0066667)⁻⁶⁰] ≈ $405.53 per month after rounding to cents.
3. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

At these inputs, the estimated payment is $405.53 per month, and total interest is $4,331.80. The payment amount is rounded before total interest is calculated, so the result follows the calculator’s stated convention.

Assumptions

• The interest rate stays fixed for the full loan term.
• Payments are equal monthly payments, made at the end of each monthly period.
• Interest accrues monthly using APR divided by 12.
• The estimate excludes fees, taxes, insurance, add-on products, and other charges unless they are included in the amount borrowed.

What to Enter and How to Read the Result

Use the amount expected to be financed as the loan amount, not necessarily the vehicle’s advertised price. A down payment or trade-in value may reduce the amount borrowed; taxes, fees, or other financed charges may increase it. To estimate a particular transaction, use the amount and terms supplied in its written loan figures rather than assuming those items are included automatically.

APR is entered as a yearly percentage, such as 8 for 8%, not as 0.08. The calculator divides it by 1200 to convert that percentage to a monthly decimal rate. The term is in years: five means 60 monthly payments. Use the lender’s quoted APR and term as inputs when available; the default values are only an example, not a statement about rates or loan availability.

The first result is the scheduled principal-and-interest payment under the formula. The second is the sum of those rounded payments minus the original principal. It is not the total cost of owning or operating a car. Fuel, maintenance, repairs, registration, insurance, and other ownership expenses are outside the calculation.

How Loan Amount, APR, and Term Affect Payments

For the same rate and term, borrowing more increases the payment. For the same principal and term, a higher APR increases the payment and usually increases the total interest calculated by this model. These are mathematical relationships, not a prediction of what a lender will offer.

Lengthening the term generally lowers the scheduled monthly payment because the principal is spread across more installments. However, it also means interest accrues for more months, so the total interest can rise. A payment figure alone therefore does not show how much will be repaid overall. Compare the payment, number of payments, total repayment, and any charges shown in the lender’s disclosure.

Common Mistakes and Calculator Limits

• Confusing price with principal: The calculation uses the amount financed. A down payment, trade-in, or financed charges can make that different from the vehicle price.
• Entering APR in the wrong format: Enter 8 for 8%, not 0.08. The calculator handles the conversion.
• Mixing months and years: Enter the term in years. For example, a 48-month term is four years.
• Expecting an exact lender quote: The formula models equal payments at a fixed rate. Actual contract details, payment dates, fees, and rounding practices may differ.
• Ignoring a changing rate or irregular payments: This calculator does not model variable rates, skipped or extra payments, a balloon payment, or a payment schedule that differs from monthly installments.

Because the payment is rounded to cents, multiplying that payment by the number of installments can produce a slightly different total than calculations that retain unrounded amounts internally. This page intentionally uses the rounded payment to calculate total interest. The APR and amount entered should also be checked against the figures supplied for the specific loan; the calculator cannot determine eligibility, approval, or the terms a lender may provide.

Frequently Asked Questions

How do I calculate a monthly car payment?
Convert APR to a monthly rate by dividing it by 1200, convert the term to months, and apply the fixed-payment formula shown above to the amount financed. The calculator performs those steps and rounds the payment to cents.

Does a car payment calculator include taxes and insurance?
Not in this calculation. It estimates principal and interest only. Include taxes or fees in the loan amount only if they will be financed, and account separately for insurance and other ownership costs.

Should I enter the car price or the amount financed?
Enter the amount expected to be borrowed. It may differ from the vehicle price after a down payment, trade-in, taxes, fees, or other financed items are accounted for.

Why does a longer car loan have a lower monthly payment?
A longer term spreads repayment over more monthly installments. Since interest is calculated over more periods, a lower monthly payment does not necessarily mean less interest overall.

Is the calculator’s result the exact payment a lender will charge?
No. It is an estimate based on a fixed rate, monthly payments, and the stated formula. Contract-specific amounts, payment timing, and lender calculations can change the figures; the lender’s disclosure gives the exact figures.

This result is an estimate, and 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