N.Y. GCM Law § 27

§ 27. Net income defined; computation. The term "net income" means the\ngross income of a taxpayer less the deductions allowed by this subpart.\n The net income shall be computed in accordance with the method of\naccounting regularly employed in keeping the books of such taxpayer; but\nif no such method of accounting has been so employed, or if the method\nemployed does not clearly reflect the income, the computation shall be\nmade upon such basis and in such manner as in the opinion of the\ndirector of finance does clearly reflect the income. In determining net\nincome, war losses, taxation of property recovered, and basis of\nproperty shall be treated in substantially the same manner as such\nlosses, recoveries and basis are treated under the applicable provisions\nof section thirteen hundred thirty-one of the internal revenue code.\n