N.J. Admin. Code § 18:26-10.13
If the Inheritance Tax Branch takes more than six months to remit a valid refund after a refund application or written request is received by the Director, taxpayers have the right to receive interest on the refund. If interest must be paid, it will be calculated to accrue from the date of filing of a refund claim, the date of tax is paid in accordance with 18:26-8.6, or the due date of the return, whichever is later. Interest will be paid at a rate determined by the Director to be equal to the prime rate, determined for each month or fraction thereof, compounded annually at the end of each calendar year, from the date that such interest commences to accrue to the date of the refund. This rule becomes effective for returns due on and after January 1, 1994. No interest will be paid on an overpayment of less than one dollar ($ 1.00), or on an overpayment refunded within six months after the last date prescribed or permitted by extension of time for filing the return, or within six months after the return is filed, whichever is later. No interest will be paid on an overpayment unless the taxpayer files a claim for refund.
N.J. Admin. Code § 18:26-10.13