Car Refinance Loan Calculator: Payment and Interest

A car refinance loan calculator estimates your monthly payment and total interest from the amount refinanced, APR, and loan term. Enter those figures to see the scheduled payment and interest over the full term; it does not predict a lender’s offer or include costs that are not entered.

Formula

The calculator uses the standard fixed-payment loan formula. It converts annual APR to a monthly rate and spreads repayment across the number of monthly payments:

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

• P is the loan amount being refinanced, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1,200. For an 8% APR, r = 8 ÷ 1,200.
• n is the term in months: years × 12.

Total interest is calculated as monthly payment × n − P. The payment is displayed to the nearest cent, and total interest uses that rounded payment. Because APR must be above zero for this formula, the calculator accepts rates from 0.01% to 100%.

Worked Example

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

1. Convert the APR to a monthly decimal rate: r = 8 ÷ 1,200 = 0.0066667.
2. Convert the term to months: n = 5 × 12 = 60.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53 per month, rounded to cents.
4. Calculate interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80 total interest.

These are estimates for equal monthly payments under the stated assumptions. A lender’s payment schedule may differ if the financed amount, payment dates, fees, or other contract terms differ.

Assumptions

• The APR and payment amount stay fixed throughout the modeled term.
• Payments are monthly, with the first payment one month after the loan begins.
• Interest compounds monthly at APR ÷ 12, represented as APR ÷ 1,200 in the formula.
• The estimate excludes fees, taxes, insurance, and other costs unless they are included in the loan amount entered.

Using the Calculator for a Car Refinance

Enter the amount that would actually be financed under the proposed refinance, not automatically the car’s original purchase price. A current payoff quote can differ from the balance shown on an older statement because interest may accrue between statement and payoff dates. If a lender’s written offer rolls eligible costs into the new loan, include them in the amount only when they are part of the financed balance.

Use the APR and term shown in the offer you are evaluating. APR is an annualized cost measure, while the formula turns it into a monthly rate for payment arithmetic. The calculator does not find an available APR, estimate credit eligibility, or account for a lender’s underwriting decisions. Get the exact rate, financed amount, term, and payment schedule from the lender’s disclosure.

The displayed payment is the scheduled principal-and-interest payment under the formula. It is not necessarily the full monthly cost of owning the vehicle: insurance, maintenance, registration, and any other bills are separate. Similarly, the total interest figure is not the total amount of every expense associated with the car.

How to Read the Results

The monthly payment answers how much the modeled loan requires each month if payments are level and made on schedule. Total interest shows the interest implied by making all scheduled payments through the end of the term. Add the principal to that interest to get the modeled total of payments: in the example, $20,000 + $4,331.80 = $24,331.80.

Changing the term changes both the monthly payment and the number of months over which interest accrues. A longer term generally lowers the calculated payment for the same principal and APR, but it also means more payment periods; a shorter term has fewer periods and a higher scheduled payment. The exact effect depends on the inputs. Compare the full payment schedule and total costs rather than interpreting a smaller monthly figure by itself.

Common Mistakes and Limits

• Using the wrong balance: The refinance amount may differ from the original amount borrowed and from a recent account balance. Ask for a payoff figure dated for the intended transaction.
• Mixing APR and monthly rates: Enter an annual percentage, such as 8, not 0.08 or the monthly decimal 0.0066667. The formula performs the conversion.
• Confusing term units: Enter years, such as 5 for five years. The calculator converts years to months.
• Overlooking added costs: If costs are financed, they increase the amount on which the model calculates interest. Costs paid separately are not reflected in this payment or interest estimate.
• Expecting exact contract figures: Rounding to cents, payment dates, daily interest calculations, and contract-specific terms can make actual figures differ.

This is a simplified level-payment model. It does not model an existing loan’s remaining schedule, unpaid interest or fees, a changing rate, skipped or late payments, extra principal payments, or a vehicle’s value. To compare a current loan with a proposed refinance, obtain the current payoff and remaining schedule as well as the proposed loan’s complete terms; this calculator alone does not decide whether refinancing is appropriate.

Frequently Asked Questions

How do I calculate a car refinance payment with interest?
Convert APR to a monthly decimal by dividing it by 1,200, convert the term to months, then use the fixed-payment formula shown above. The calculator carries out those steps and estimates total interest.

Does the calculator include the existing loan payoff?
No. Enter the amount to be financed in the new loan. Use a current payoff quote to identify that amount; the calculator does not retrieve or calculate a lender’s payoff figure.

Why can the refinance payment differ from my current payment?
The new loan amount, APR, or remaining term may differ from the current loan’s figures. Fees included in the new balance and payment timing can also affect the actual amount due.

Does a longer car refinance term reduce total interest?
Not necessarily. A longer term can reduce the modeled monthly payment, but it adds payment periods. Total interest depends on the principal, APR, and term together, so compare the calculated total and the written offer’s complete terms.

Is APR the same as the monthly interest rate?
No. APR is entered as an annual percentage. This calculator uses APR ÷ 1,200 as the monthly rate for its monthly-payment formula; a lender’s disclosures determine the exact contract calculations.

The 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 | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2