N.J. Stat. § 18A:24-73
The issuing board shall annually cause to be made calculations of the average amount of the principal of bonds issued and outstanding under this act and of the average amount of the reserve provided for in section 6, for the 12-month period prior to such calculation. The calculations shall be made not more than 3 months prior to the date for the publication of the annual school budget. Said budget shall contain provision, as a mandatory item, of an amount equal to that sum which would be sufficient as a level annual installment to retire in full the net amount resulting from the subtraction of the average reserve from the average outstanding principal, at that rate of interest that would be applicable if all bonds were held to maturity, if such installments were paid over the full term of the blanket bond. The amount annually required for said item shall be placed in a separate sinking fund to be invested and reinvested in the same manner as provided in section 6, and shall be applied only to the satisfaction of bonds outstanding at the maturity of the last blanket bond. Any excess, remaining after full satisfaction of such bonds, or the making of provisions therefor, shall be and become general funds available to the issuing board but for authorized school purposes only.
N.J.S. § 18A:24-73