Installment due dates.
Taxpayers shall make estimated payments in 4 installments, on or before the 15th day of each of the following months:
(a)#
The 4th month of the taxable year.
(b)#
The 6th month of the taxable year.
(c)#
The 9th month of the taxable year.
(d)#
The first month of the next taxable year.