Auto Loan Refinance Calculator: Estimate Payments

An auto loan refinance calculator estimates a replacement loan’s monthly payment and total interest from the amount refinanced, APR, and term. Enter the proposed loan’s figures to see the payment estimate and compare it with your current loan; the calculation does not include lender fees or determine whether you qualify.

Formula

The calculator uses the standard fixed-payment loan formula. First, it converts the annual percentage rate into a monthly rate and converts the term into a number of monthly payments. It then calculates the payment that amortizes the entered principal over that term:

• Monthly payment: M = P × r ÷ [1 − (1 + r)⁻ⁿ]
• Total interest: I = (M × n) − P
• Monthly rate: r = APR ÷ 1,200
• Number of payments: n = years × 12

Here, P is the new loan amount in dollars, APR is the entered annual percentage rate, r is the monthly rate as a decimal, n is the number of monthly payments, M is the monthly payment in dollars, and I is total interest in dollars. The calculator treats the entered APR as a fixed rate for the full term. Its interest result is calculated using the displayed monthly payment rounded to cents.

Worked Example

Using the calculator’s default inputs: a $20,000 loan, 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. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰] = approximately $405.53 per month, rounded to cents.
4. Calculate total interest using the displayed payment: $405.53 × 60 − $20,000 = $4,331.80.

The estimated payment is $405.53 per month, and estimated total interest is $4,331.80. A lender’s actual payment can differ if the financed amount, rate, payment schedule, or fees differ.

Assumptions

• The replacement loan has a fixed APR throughout the entered term.
• Payments are equal monthly payments, made at the end of each monthly period.
• Interest is compounded monthly using APR divided by 12.
• The calculation excludes fees, taxes, insurance, and other charges unless they are included in the loan amount you enter.

How to Use the Estimate When Refinancing

For a refinance estimate, the loan amount should reflect the amount you expect to finance, not automatically the car’s original purchase price. A starting point is the current payoff figure from the existing loan, adjusted for any amount you plan to include in the new loan. The payoff figure may differ from the balance on a recent statement because interest can accrue between statement and payoff dates. Ask the current servicer for a payoff quote and the date through which it applies.

Enter the proposed APR and term from the refinancing offer or a clearly identified estimate. These are inputs, not predictions: the calculator cannot supply a lender’s rate or fees. If a fee is financed, including it in the loan amount can show its effect on the payment and interest, but it does not identify every charge in an offer.

To compare the estimate with the existing loan, use the current remaining balance, APR, and months remaining to estimate the current payment and remaining interest on the same basis. Compare more than the monthly payment. Extending the term can lower the payment while increasing the time debt remains outstanding and potentially increasing total interest. A shorter term can raise the payment even when the total interest estimate falls. These are arithmetic effects, not a recommendation about which loan to choose.

Reading the Results and Common Mistakes

• Payment is not total borrowing cost. The monthly payment is the regular principal-and-interest estimate. Total interest is the interest over the modeled term; neither figure includes excluded fees or optional products.
• Use the remaining loan amount. Entering the original purchase price instead of the current payoff amount can make a refinance estimate substantially inaccurate.
• Keep APR and term units straight. APR is entered as a percentage per year, such as 8 for 8%, while term is entered in years. Do not enter 0.08 for an 8% APR.
• Account for rounding. Payments are rounded to cents, while a real lender may adjust the final payment or use its own day-count and rounding procedures.
• Do not treat the result as an offer. The calculator does not assess credit, vehicle value, loan eligibility, payoff timing, or lender-specific requirements.

A refinance may also change how much of each payment goes to interest versus principal because the new loan starts with a new amortization schedule. The calculator shows the payment and total interest for the proposed loan, but it does not calculate the current loan’s payoff path or add one-time costs. For a full comparison, collect the current payoff amount and remaining schedule, plus the proposed loan’s itemized terms and charges.

What This Calculator Does Not Include

This tool models one loan with a fixed APR and equal monthly payments. It does not calculate a variable rate, irregular payment dates, skipped or extra payments, late charges, prepayment charges, or the payoff balance on a particular date. It also cannot tell whether a vehicle’s value or condition meets a lender’s criteria. If fees are paid up front rather than financed, they will not appear in the payment or total-interest result; consider them separately when comparing figures.

For precise numbers, use the principal, APR, term, and charges shown in the proposed lender disclosure. A different amount financed or payment schedule can change the result even when the quoted APR looks similar.

Frequently Asked Questions

How do I calculate a car refinance payment?
Enter the amount to refinance, the proposed APR as a percent per year, and the term in years. The calculator converts the APR to a monthly rate and applies the fixed-payment loan formula.

Should I use my current balance or payoff amount?
For an estimate of a replacement loan, use the amount expected to be financed. A dated payoff quote from the current servicer is generally more relevant than an older statement balance because the figures can change with accrued interest and timing.

Does refinancing always lower the monthly payment?
No. The result depends on the new principal, APR, and term. A shorter term or a higher amount financed can produce a higher payment; a longer term can reduce the payment while extending repayment.

Does this calculator include refinance fees?
No. It excludes fees unless you add a financed fee to the loan amount. Fees paid separately are not included in either displayed result.

Why does my lender’s payment differ from the estimate?
The lender may use a different amount financed, payment date, APR, rounding method, or charge structure. Check the lender’s disclosure for the exact terms and payment schedule.

This result is an estimate for educational purposes, 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