Auto Loan Refinance Calculator: Compare Payments

An auto loan refinance calculator estimates a new monthly payment and total interest from the balance you plan to refinance, the new APR, and the new loan term. Enter those figures to see the payment and interest under a fixed-rate estimate; compare them with your current loan using its lender-provided figures.

Formula

The calculator uses the standard fixed-payment loan formula. It converts the annual percentage rate (APR) to a monthly rate, then calculates the level monthly payment needed to repay the entered principal over the term.

• Monthly payment: P × r ÷ [1 − (1 + r)⁻ⁿ]
• Total interest estimate: M × n − P

P is the amount refinanced, in dollars; APR is the annual percentage rate, entered as a percentage; r is the monthly rate, APR ÷ 1,200; n is the number of monthly payments, equal to years × 12; and M is the monthly payment in dollars. The payment is rounded to cents before total interest is calculated. The result assumes the same payment amount throughout and does not model a changing rate.

Worked Example

Using the calculator’s defaults—$20,000 principal, 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 months: 5 × 12 = 60.
3. Substitute into the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] ≈ $405.53 per month.
4. Calculate total interest using the rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

The calculator therefore displays a monthly payment of $405.53 and estimated total interest of $4,331.80. Actual lender figures can differ because of rounding, payment dates, fees, or other loan terms.

Assumptions

• The interest rate is fixed for the entire entered term.
• Payments are level monthly payments, made at regular intervals; the first payment is treated as one month after the loan begins.
• Interest compounds monthly at APR divided by 12.
• Fees, taxes, insurance, optional products, and other amounts added to a loan are not included unless reflected in the principal you enter.

What Auto Loan Refinancing Means

Refinancing an auto loan means replacing an existing loan with a new one, generally using the new loan’s proceeds to pay off the old balance. The borrower then makes payments under the new contract. A calculator can estimate the payment on that new balance, but it cannot establish whether a lender will offer a particular rate, term, or amount.

Use the current payoff amount—not necessarily the original amount borrowed—as the starting principal. A payoff quote may include interest accrued since the last payment and may be valid only through a specified date. Ask the current loan servicer for the amount and date it applies to, and obtain the proposed new loan’s APR, term, payment, and itemized charges from the prospective lender. Enter any charges that are financed as part of the loan in the principal; do not count them twice.

How to Compare the Estimate

A lower monthly payment by itself does not show the full cost of refinancing. The payment can fall because the new APR is lower, because the term is longer, or because both change. A longer repayment period can mean more payments and more interest overall, even if each payment is smaller.

For a useful comparison, gather the current loan’s remaining balance, APR, payment, and remaining number of payments, as well as the new offer’s corresponding figures and any charges. Compare remaining costs from today—not the original loan’s total interest, which includes payments already made. Keep the comparison periods clear: this calculator reports interest over the new term, not a complete side-by-side analysis of two loans.

For example, if a new five-year term produces a smaller payment than a current loan with fewer months left, the difference may reflect spreading repayment over more time. Check both the total of remaining current payments and the total of new payments plus any costs paid separately. This arithmetic is only a comparison framework; lender disclosures define the actual amounts and payment schedule.

Limits and Common Pitfalls

• Using the wrong balance: The car’s value, original loan amount, and payoff amount are different figures. Use the proposed amount being financed.
• Ignoring costs: A fee paid upfront affects the overall comparison even if it does not appear in the payment formula. A fee financed into the principal raises the estimated payment and interest.
• Comparing payment alone: Include the number of payments and all applicable charges when reviewing total cost.
• Entering a quoted rate as a decimal: Enter 8 for 8% APR, not 0.08. The calculator converts a percent to a monthly rate internally.
• Assuming approval or exact payoff: The calculator does not evaluate eligibility, vehicle details, lender conditions, or the old loan’s payoff process.

The standard formula is designed for a fixed rate and regular level payments. It does not model irregular payment dates, a changing interest rate, a balloon amount, or contract-specific calculations. Rounding each payment to cents can also make the final amount differ slightly from a lender’s schedule.

Frequently Asked Questions

What information do I need to estimate an auto refinance payment?
Enter the amount to be refinanced, the proposed APR, and the new term. For a real comparison, also obtain the current loan’s payoff amount and remaining payment schedule, plus the new loan’s disclosed costs.

Does refinancing always lower the monthly payment?
No. The estimated payment depends on the principal, APR, and repayment term. A changed balance, rate, or term can increase or decrease it; this calculator does not predict a lender’s offer.

Can a lower payment mean I pay more overall?
Yes. Extending the term can reduce each payment while increasing the number of payments and potentially the total interest. Compare the remaining cost of both loans and account for charges.

Does this calculator include refinance fees?
No separate fee input is provided. Include charges in the principal only if they are financed into the new loan; consider separately paid costs in your own comparison.

Is the result my exact lender payment?
No. It is an estimate under the stated fixed-rate, monthly-payment assumptions. The lender’s contract and disclosure provide the exact payment and totals.

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

Related

• Loan Balance Letter: What It Shows and How to Read It
• Loan Balance Calculator: See What You Still Owe
• Loan Balance Formula: Calculate What You Still Owe

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