Tax Guide, State Taxes
New York State Residency Rules 

Nonresident
You are a New York State nonresident if you were not a resident of New York State for any part of the year. 

Undergraduate Students:  A residence maintained by a full-time student enrolled at an institution of higher education in an undergraduate degree program leading to a baccalaureate degree and occupied by the student while attending the institution is not a permanent place of abode with respect to that student.  As such, an undergraduate student who lived in New York all year may be able to file as a New York nonresident if New York was not his/her domicile.

NY Nonresident Income Allocation Worksheet:  If you worked for a New York employer while living in another state (NJ, CT, etc.), and you had business days (required by your employer), worked outside New York State, you will only pay New York tax on the wages earned while physically working in New York.  If you were working a significant number of days in another state, you may owe tax to that state.  

Resident
You are a New York State resident for income tax purposes if:
•  You maintain a permanent place of abode in New York State for substantially all of the taxable year and spend 184 days or more in New York State during the taxable year, whether or not you are domiciled in New York State for any portion of the taxable year. Note: Any part of a day is a day for this purpose.  There are exceptions for members of the armed forces; or
• Your domicile is New York State. However, even if your domicile is New York, you are not a resident if you meet all three of the conditions in either Group A or Group B as follows:
Group A
1) You did not maintain any permanent place of abode in New York State during the tax year; and
2) You maintained a permanent place of abode outside New York State during the entire tax year; and
3) You spent 30 days or less (any part of a day is a day for this purpose) in New York State during the tax year.
Group B
1) You were in a foreign country for at least 450 days (any part of a day is a day for this purpose) during any period of 548 consecutive days; and
2) You, your spouse (unless legally separated), and minor children spent 90 days or less (any part of a day is a day for this purpose) in New York State during this 548-day period; and
3) During the nonresident portion of the tax year in which the 548‑day period begins, and during the nonresident portion of the tax year in which the 548‑day period ends, you were present in New York State for no more than the number of days which bears the same ratio to 90 as the number of days in such portion of the tax year bears to 548. The following formula illustrates this condition:

Number of days in the                  Maximum number     
nonresident portion        × 90   =  of days allowed
548                                            in New York State

Statutory Resident:  The definition of resident individual for New York State income tax purposes was clarified (under section 605(b)(1)(B) of the New York Tax Law) to state that an individual who maintains a permanent place of abode in New York State and spends more than 183 days of the tax year in New York State, whether or not they are domiciled in this state, is a statutory resident unless they were in active service in the military.

Domicile is defined as your permanent home, the place you always intend to return to, regardless of where you may be at the present time.  For a person in the U.S. on a temporary visa, domicile is usually their home country.  You can have only one domicile.

A place of abode.   In general, a permanent place of abode is a residence (a building or structure where a person can live) that you permanently maintain, whether you own it or not, that is suitable for year-round use. A permanent place of abode usually includes a residence your spouse owns or leases.

Part-year resident
You are a New York State part-year resident if you meet the definition of resident or nonresident for only part of the year

The difference in tax between filing as nonresident vs. resident

As a resident, you pay state and city tax on all your income.  As a non-resident, you only pay tax on New York source income, which includes earnings from work physically performed in New York State, and income from real property.  You are not liable for city tax.  Generally, if you live in New York City, you will have city tax withheld from each paycheck (as reported on the W-2), which is why you may receive a much larger tax refund (getting all or most of the city tax back) if you file as a nonresident.