Auto Loan Payoff Calculator
Pay off your car loan faster with extra payments.
Result
How it is calculated
The tool adds your regular and extra payment, pay = payment + extra, and uses the monthly rate i = annual rate / 100 / 12. The number of months to reach a zero balance is n = −ln(1 − B·i / pay) / ln(1 + i), where B is the balance. Total paid is pay × n and total interest is pay × n − B. At a 0% rate it is simply B / pay. Months are not rounded up to a whole number, so a result such as 40.2 means the last payment is a partial one. If the combined payment does not exceed the first month's interest, the balance never falls and no result is shown. A balance of zero or less, or a negative payment, also gives no result, and the extra payment field must hold a number (use 0 for none). It shows one scenario, not a comparison.
Worked example
The balance is $18,000 at 6.5% a year, with a $400 monthly payment and $100 extra, so pay = $500. The monthly rate is 6.5 / 100 / 12 = 0.5417%. Then n = −ln(1 − 18,000 × 0.005417 / 500) / ln(1.005417), which the tool shows as 40.2 mo. Total paid is 500 × 40.15 = $20,076.92, so the interest is $2,076.92. Running the same loan with 0 extra gives 51.7 mo and $2,687.21 of interest, so the $100 extra saves about 11.5 months and $610.29.
Common mistakes
- Leaving the extra payment empty. The tool needs a number there and shows no result otherwise, so enter 0 when you want the plain schedule.
- Entering a monthly payment that is too low. If payment plus extra does not exceed the first month's interest, the balance never falls and there is no result.
- Using the original loan amount instead of today's balance. The calculation starts from the balance you enter, so use the current payoff figure.
- Entering the rate as a decimal (0.065). The field takes a percentage, so type 6.5.
- Expecting the tool to show the saving by itself. It reports one scenario, so run it twice, with and without the extra payment, and compare. Fees, prepayment penalties or a payoff quote from the lender are not included.
About this calculator
An auto loan amortizes like any installment loan: each payment covers that period's interest first, with the remainder reducing principal. Adding extra payments — applied directly to principal — shrinks the balance faster than the schedule assumes, which means every future payment carries less interest, compounding the savings over the life of the loan.
This calculator takes your loan balance, interest rate, and regular payment, plus an extra payment amount, and shows how many months it takes to pay off the car and the total paid and total interest at that combined payment. To see how much sooner you'd finish and how much interest you'd save, run it twice, once with the extra payment set to 0 and once with your extra amount, and compare the two. It's the calculation borrowers use to decide whether directing spare cash toward the car loan is worth it before committing to it as a habit.
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