N.J. Admin. Code § 18:2-2.11
For the purposes of determining the interest charge to be assessed against a taxpayer, prime rate shall mean the average predominant prime rate, as determined by the Board of Governors of the Federal Reserve System, quoted by commercial banks to large businesses as of the first business day of the calendar quarter immediately preceding the quarter within which the tax or payment became due. The applicable rate shall be adjusted on the first business day of each quarter thereafter over the life of the debt. Prime rate means the rate quoted as of December 1 of the calendar year immediately preceding the calendar year in which the payment was due; provided, however, that if the Director determines that the prime rate quoted by commercial banks to large businesses varies by more than one percentage point from the rate otherwise determined, the Director shall redetermine the prime rate to be that quoted prime rate for subsequent calendar quarters of the calendar year in which payments become due.
N.J. Admin. Code § 18:2-2.11