N.Y. Comp. Codes R. & Regs. tit. 20, § 3-6.5
Tax Law, § 210(2)
If a period covered by a report is other than 12 calendar months, the amount of subsidiary capital is determined by multiplying its average value (see section 3-6.4 of this Subpart), by the number of calendar months or major parts thereof included in such period, and dividing the product by 12.