Auto loan refinance calculator

What is an auto loan refinance calculator?

An auto loan refinance calculator is a free online tool that estimates what happens to your car payment when you replace your existing loan with a new one. Refinancing means taking out a fresh loan to pay off the balance you still owe, usually to secure a lower interest rate, a different term, or both. By entering the balance remaining on your current loan, the monthly payment you make today, and the rate and length of the loan you are considering, you can see your new monthly payment, how much you would save each month, and the total interest and total payments on the new loan before you apply.

How does it work?

You provide four pieces of information:

• The remaining loan balance — the amount you still owe on your current car loan, not the original amount you borrowed.
• Your current monthly payment — what you pay each month right now, used to work out your savings.
• The new annual interest rate offered by the lender you are considering, as a percentage.
• The new loan term, in months.

The calculator treats your remaining balance as the principal of a brand-new loan. It converts the new annual rate into a monthly rate and applies the standard amortization formula to find a level monthly payment. Subtracting that new payment from your current payment gives your monthly savings, and multiplying the new payment across the full term reveals the total you would pay and the interest hidden inside it.

Formula

The new monthly interest rate is the new annual rate divided by 12:

$r = \frac{\text{new annual rate}}{100 \times 12}$

With a remaining balance $B$ spread over $n$ monthly payments, the new level monthly payment $M$ is:

$M = \frac{B \cdot r \cdot (1 + r)^{n}}{(1 + r)^{n} - 1}$

When the new rate is zero, this simplifies to:

$M = \frac{B}{n}$

Your monthly savings compared with the current payment $C$ are:

$\text{savings} = C - M$

The total of payments on the new loan is $M \cdot n$, and the total interest is $M \cdot n - B$.

Worked example

Suppose you still owe $20,000 on your car, you currently pay $500 a month, and a lender offers you a 4% annual rate over a new 48-month term:

• New monthly rate $r$ = 0.04 / 12 ≈ 0.003333
• Remaining balance $B$ = 20000, term $n$ = 48

Calculation:

$M = \frac{20000 \cdot 0.003333 \cdot (1.003333)^{48}}{(1.003333)^{48} - 1} \approx 451.58$

The new monthly payment is about $451.58, which is roughly $48.42 less than your current $500 payment. Over the 48 months you would pay about $21,675.84 in total, of which about $1,675.84 is interest.

Notes

The calculator assumes a fixed interest rate and equal monthly payments, which is the most common structure for a refinanced car loan. It uses your remaining balance as the amount financed, so make sure you enter the current payoff figure from your lender rather than the price of the car or the amount you originally borrowed.

The monthly savings shown here compare only the payment amounts. A lower payment achieved by stretching the term over more months can still increase the total interest you pay, so it is worth checking the total interest figure alongside the savings. The estimate also excludes any prepayment penalties on your existing loan, title transfer fees, or other refinancing costs, which reduce the real benefit of switching. Comparing the total of payments on the new loan with what remains on your current one is the clearest way to judge whether refinancing is worth it.

FAQs

Does a lower monthly payment always mean I save money?

Not necessarily. Extending the term lowers each payment but can raise the total interest you pay over the life of the loan. Look at both the monthly savings and the total interest before deciding — a smaller payment spread over many more months may cost more overall.

What balance should I enter?

Enter the current payoff balance on your existing loan, which you can get from your lender. This is usually less than the amount you originally financed and is the figure a new lender would pay off when you refinance.

Will refinancing hurt my finances if rates have not dropped?

If the new rate is not lower than your current one, refinancing mainly changes the term rather than the cost. A longer term at the same rate reduces the payment but increases total interest, while a shorter term raises the payment and cuts interest. The calculator lets you test each scenario before committing.