N.J. Stat. § 17:16C-44
The holder of a retail installment contract may extend the scheduled due date of any retail installment contract and defer the scheduled due date of any or all installment payments, or reduce the amount of any or all installments and may, as a consideration therefor, make a total additional charge not to exceed the amount ascertained under either of the following methods of computation at the respective rates indicated by the following options:
Option 1. The additional charge shall be computed on the amount of the scheduled installment or installments extended, deferred or reduced for the period or periods for which each installment or part thereof is extended, deferred or reduced at the following rates on contracts originally in the respective classifications set forth in section 41 of this act:
Class I. 1% per month;
Class II. 1 1/2% per month;
Class III. 2% per month;
Class IV. 2% per month;
Option 2. The holder of a retail installment contract by written agreement may renew the entire unpaid balance on any retail installment contract and may make a charge therefor at the rates charged in the original contract from the date of renewal to the maturity of the final installment. The amount of the balance to be renewed shall be obtained by adding to the existing unpaid balance on the original contract, the cost of any insurance or other benefits for the period of the extension and any accrued default charges and refunding the unearned portion of the time price differential charged according to the formula provided in section 43 of this act; provided, however, that in computing the unearned time price differential charge no allowance shall be taken for the amount of the acquisition cost permitted therein.
N.J.S. § 17:16C-44