N.Y. GCM Law § 121

§ 121. Accounting periods and methods. (a) Accounting periods.--A\ntaxpayer's taxable year under this title shall be the same as the\ntaxpayer's taxable year for federal income tax purposes.\n (b) Accounting methods.--A taxpayer's method of accounting under this\ntitle shall be the same as the taxpayer's method of accounting for\nfederal income tax purposes. In the absence of any method of accounting\nfor federal income tax purposes, unincorporated business taxable income\nshall be computed under such method as in the opinion of the director of\nfinance clearly reflects income.\n (c) Change of accounting period or method.--(1) If a taxpayer's\ntaxable year or method of accounting is changed for federal income tax\npurposes, the taxable year or method of accounting for purposes of this\ntitle shall be similarly changed.\n (2) If a taxpayer's method of accounting is changed, other than from\nan accrual to an installment method, any additional tax which results\nfrom adjustments determined to be necessary solely by reason of the\nchange shall not be greater than if such adjustments were ratably\nallocated and included for the taxable year of the change and the\npreceding taxable years, not in excess of two, beginning after January\nfirst, nineteen hundred sixty-six, during which the taxpayer used the\nmethod of accounting from which the change is made.\n (3) If a taxpayer's method of accounting is changed from an accrual to\nan installment method, any additional tax for the year of such change of\nmethod and for any subsequent year which is attributable to the receipt\nof installment payments properly accrued in a prior year, shall be\nreduced by the portion of tax for any prior taxable year attributable to\nthe accrual of such installment payments, in accordance with regulations\nof the director of finance.\n