N.J. Stat. § 17:16C-43
When the balance owing on a retail installment contract is repaid in full at any time before the end of the contract period, the holder of the contract shall allow a credit on account of the time price differential, the amount of which shall be determined by the application of the formula C = AN / D, in which "C" represents the amount of the credit to be given; "A" represents the amount of the time price differential, less an acquisition cost of $15.00; "D" represents an amount determined as follows: there shall be ascribed to each payment-period included in the contract period, beginning with the first payment-period scheduled by the contract, the cardinal number descriptive of the number of payment-periods scheduled by the contract to elapse from the beginning of each such payment-period to the end of the contract period, and the sum of all such cardinal numbers shall constitute the quantity "D" ; and "N" represents the difference between the quantity "D" and the sum of all the cardinal numbers ascribed to the payment-periods which have elapsed, in whole or in part, from the date of the contract to the date upon which such repayment is made. This section shall not apply when the amount of the credit is less than $1.00.
N.J.S. § 17:16C-43