In the case of an individual on the fiscal year basis, the dates prescribed for payment of the estimated tax shall be the 15th day of the 4th month, the 15th day of the 6th month, and the 15th day of the 9th month of the taxable year and the 15th day of the 1st month of the succeeding taxable year. For example, if an individual having a fiscal year ending on June 30, 1956, first meets the requirements of section 6015(a) on January 15, 1956, and the declaration is filed on or before March 15, 1956, the estimated tax shall be paid in 2 equal installments, one at the time of filing of such declaration and the other on or before July 15, 1956.
26 C.F.R. §1.6153-2