N.Y. Comp. Codes R. & Regs. tit. 20, § 18-5.7 – Adjusting taxable assets to period covered by return.

(a) If the period covered by the taxpayer's return is other than 12 calendar months, the taxpayer's taxable assets must be prorated to correspond with the period covered by the return under article 32 of the Tax Law. The prorated taxable assets are determined as follows:
1. (1) compute taxable assets in the manner set forth in section 18-5.2 of this Subpart;
2. (2) divide taxable assets by 12; and
3. (3) multiply the result by the number of calendar months, or major parts thereof, covered by the return under article 32 of the Tax Law.
(b) The method of computing taxable assets for a short period, as set forth in this section, applies to taxpayers reporting on either a calendar-year or fiscal-year basis for Federal income tax purposes.
(c) If, in the opinion of the Tax Commission, the method described in this section does not properly reflect the taxpayer's taxable assets for purposes of article 32 of the Tax Law during the period covered by its return, the Tax Commission may determine taxable assets solely on the basis of the taxpayer's assets during such period.