New Jersey Statutes Title 54. Taxation 54 § 10A-19

The director may grant a reasonable extension of time for the filing of returns or the payment of tax or both, under such rules and regulations as he shall prescribe, which rules and regulations may require the filing of a tentative return and the payment of an estimated tax. If the time for filing the return shall be extended, the payment of the portion of the tax remaining to be paid, if any, shall be postponed to the date fixed by the extension of the time for the filing of the return, but in every such case the corporation shall pay, in addition to the unpaid portion of the tax, interest thereon at the rate as provided in the State Tax Uniform Procedure Law, R.S.54:48-1 et seq., from the time when the return originally was required to be filed to the date of actual payment under the extension; provided, that if such unpaid portion of the tax is not paid within the time fixed under the extension, the interest on such unpaid portion shall be computed at the rate as provided in the State Tax Uniform Procedure Law, R.S.54:48-1 et seq., from the date the tax was originally due to the date of actual payment and if the amounts paid up to and including the time of the filing of the tentative return total less than the lesser of: 90% of the amount due; or for a taxpayer that had a preceding fiscal or calendar accounting year of 12 months and filed a return for that year showing a liability for tax, an amount equal to the tax computed at the rates applicable to the current fiscal or calendar accounting year but otherwise on the basis of the facts shown on the return of the taxpayer for, and the law applicable to, the preceding fiscal or calendar accounting year, the taxpayer shall be liable for a penalty of 5% per month or fraction thereof on the amount of underpayment, not to exceed 25% of that underpayment, which shall be in addition to the interest charges provided above.