Car Loan Calculator Payment and Interest Amount

A car loan calculator estimates your monthly payment and the total interest paid using the loan amount, APR, and term. Enter those figures to see both results; the estimate assumes equal monthly payments and a fixed rate.

Formula

The calculator uses the standard fixed-payment loan formula. It first calculates the monthly payment, rounded to the nearest cent, then subtracts the amount borrowed from the sum of those rounded payments to estimate total interest.

• Monthly payment: M = P × r ÷ [1 − (1 + r)⁻ⁿ]
• Total interest: I = M × n − P
• Monthly rate: r = APR ÷ 1,200

P is the amount financed in dollars; APR is the annual percentage rate entered as a percentage; r is the monthly interest rate as a decimal; n is the term in months, calculated as years × 12; M is the monthly payment in dollars; and I is total estimated interest in dollars. The APR input must be above zero because this version uses a rate-based formula. A zero-interest loan needs a separate calculation: principal divided by the number of payments.

Worked Example

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

1. Convert the APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 months.
3. Substitute into the payment formula: M = 20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
4. The payment is $405.53 per month when rounded to cents.
5. Total of the rounded payments: $405.53 × 60 = $24,331.80.
6. Estimated interest: $24,331.80 − $20,000 = $4,331.80.

Small differences can appear if a lender calculates interest daily, rounds each installment differently, or includes costs in the amount financed. The example follows the calculator’s monthly-rate assumption and uses the rounded payment for its interest total.

Assumptions

• The APR and payment amount stay fixed over the loan term.
• Payments are equal, made once a month, with the first payment one month after borrowing.
• Interest compounds monthly using APR divided by 12.
• The calculation excludes fees, taxes, insurance, optional products, and other charges unless they are already included in the amount entered as the loan amount.

What the Payment and Interest Results Mean

The monthly payment is the scheduled amount needed to repay principal and interest over the selected term under the assumptions above. It is not necessarily the full monthly cost of owning or operating a car. Insurance, fuel, maintenance, registration, and other expenses are outside this calculation.

Total interest estimates the borrowing cost across all scheduled payments. It is not the same as the amount paid overall: add the loan principal to the interest to get the total of the modeled payments. In the example, that total is $24,331.80, of which $20,000 repays principal and $4,331.80 is interest.

At the start of an amortizing loan, a larger share of each payment generally goes toward interest because the outstanding balance is larger. As the balance falls, the interest portion typically declines and more of each payment reduces principal. The payment itself can stay level even though its allocation changes.

What to Enter for a Car Loan

Use the amount actually being financed, not automatically the vehicle’s advertised price. The financed amount may differ from the purchase price after a down payment, trade-in credit, taxes, fees, or other items are accounted for. Which costs are included depends on the transaction; use the figure supplied in the lender’s loan disclosure when available.

• Loan amount: Enter the principal being borrowed. If an amount is financed along with the car, it can increase both the payment and interest.
• APR: Enter the annual percentage rate shown for the loan, not a monthly rate. The calculator divides the percentage by 1,200 to obtain a monthly decimal rate.
• Term: Enter the repayment period in years. A five-year term, for example, means 60 monthly payments in this calculation.

For a real estimate, use figures from the same offer or disclosure. Combining a loan amount from one scenario with an APR or term from another produces a mathematical result, but not a meaningful estimate of a single loan.

How Loan Amount, APR, and Term Affect Cost

Holding the other inputs constant, a larger principal raises the payment and usually increases total interest. A higher APR also raises the payment and borrowing cost. The term has a less intuitive effect: spreading repayment over more months generally lowers the required monthly payment, but leaves the balance outstanding longer and can increase total interest.

These are formula relationships, not predictions about what rate or terms a borrower may receive. Rates, fees, and available loan terms vary by individual offer and circumstances; get the actual figures from the lender. This calculator does not assess eligibility or predict approval.

Comparing scenarios can help show the arithmetic trade-off. For example, you can enter two different terms while keeping the amount and APR unchanged, then compare the monthly payment and total interest. The calculator does not determine which scenario is appropriate for a particular budget or situation.

Common Calculation Mistakes and Limits

• Entering APR as a decimal: Type 8 for 8%, not 0.08. The formula converts a percentage to a monthly decimal.
• Using the vehicle price as principal: A down payment or trade-in can reduce the amount financed, while financed charges can raise it.
• Confusing payment with total cost: The monthly payment excludes expenses not entered, and total interest is not the same as total payments.
• Ignoring rounding: The payment is rounded to cents, and total interest uses that rounded payment multiplied by the number of months. A lender’s final installment or rounding method may differ slightly.

This is a standard fixed-rate, level-payment estimate. It does not model variable rates, irregular payment dates, extra principal payments, skipped or late payments, changing loan balances, or fees charged separately. It also does not include depreciation or the vehicle’s future value. To model extra payments or a payoff date, use a calculator designed for amortization or early payoff and supply the relevant payment details.

Frequently Asked Questions

How do I calculate a car loan payment with interest?
Convert APR to a monthly decimal by dividing it by 1,200, convert the term to months, and apply the fixed-payment formula shown above. The calculator performs those steps and rounds the monthly payment to cents.

Does total interest include the amount borrowed?
No. Interest is the borrowing cost only. Add the principal to total interest to get the modeled total of all scheduled payments.

Why is my lender’s payment different from this calculator?
The lender may use a different financed amount, payment date, rounding method, or treatment of fees. Check that the principal, APR, and term match the disclosure, and ask the lender how its quoted payment is calculated.

Does a longer car loan mean less interest?
Not necessarily. A longer term can reduce the monthly payment while increasing total interest because repayment takes longer. The exact amounts depend on the entered principal and APR.

Can I use this calculator for a zero-interest loan?
No. The formula divides by the monthly rate, so the APR must be greater than zero. For a genuine 0% rate, divide the principal by the number of monthly payments to find the level payment; modeled interest is zero if no other borrowing charges apply.

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

Related

• Auto Loan Calculator With Trade-In and Amount Owed (Negative Equity)
• Car Loan Calculator With Down Payment: Monthly Car Payment

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