Calculate loan repayment schedule, total interest, and savings from making extra payments.
Dana owes $20,000 on a 60-month car loan at 8.5%, which works out to $410.33 a month and $4,619.84 of interest over the life of the loan. If she rounds that up by $100 a month, the loan is gone in 47 months and she pays $1,109.19 less interest. This calculator reproduces both sides of that comparison for any balance, rate and term, and lists the first two years of the schedule so you can see how little of early payments goes toward principal.
Monthly payment = B × r × (1 + r)^n ÷ ((1 + r)^n − 1), where B is the loan balance, r is the annual rate ÷ 100 ÷ 12 and n is the term in months. If the rate is 0, the payment is simply B ÷ n.
Each month, interest = remaining balance × r, and the rest of the payment is principal. The extra-payment scenario repeats that loop with payment + extra every month until the balance is cleared. Interest saved = standard total interest − extra-plan interest, months saved = term − actual months, and Total Paid (Standard) is payment × term.
Worked example: B = $20,000, rate 8.5% so r = 0.085 ÷ 12 = 0.0070833, n = 60. Payment = $410.33. Month 1: interest $141.67, principal $268.66, balance $19,731.34. Month 24: interest $94.31, principal $316.02, balance $12,998.50. Over 60 payments the interest is $4,619.84 and the total paid is $24,619.84. With $100 extra the loop ends in month 47 with $3,510.64 of interest.
Rounding, daily interest accrual, a first payment with a stub period, or bundled fees and insurance are the usual causes. Compare against the total of payments on your loan disclosure.
The term field is in months. Five months on $20,000 at 8.5% is $4,085.40 a month. Enter 60 for five years.
The calculator assumes it does. Some servicers hold surplus toward the next scheduled payment unless you mark it principal-only, and that would not shorten the loan the same way.
Interest is charged on the whole balance. In month 1 it takes $141.67 of the $410.33 payment, about 35%, and by month 24 it takes only $94.31.
No, the first extra dollars work hardest. In the $20,000 example, $50 extra saves $632.08 in interest and 7 months, $100 saves $1,109.19 and 13 months, and $200 saves $1,781.54 and 22 months. Doubling the extra amount does not double the savings, because the balance shrinks faster and leaves less interest to avoid.
Not directly. The schedule assumes equal payments that fully repay the balance at the end of the term. Origination fees folded into the balance can be added to the loan amount, but a balloon payment or an interest-only period needs a different tool, and the results here would not match your contract.