NY Tax Law §1307(b)
(b) The city taxable income for the portion of the year during which an individual described in subsection (a) is a city resident individual shall be determined, except as provided in subsection (c), under the rules provided in section six hundred thirty-eight of this chapter, as if he were computing his New York taxable income and his taxable year for New York state personal income tax purposes were limited to the period of his city resident status.