951 / What is the difference between a resident alien and a nonresident alien?

A foreign individual who is not a U.S. citizen is labeled as an “alien” for U.S. tax purposes. An alien is either a nonresident alien or a resident alien. A resident alien is a foreign individual who meets either the green card test or the substantial presence test, discussed below, and a nonresident alien is any other foreign individual unless that individual is otherwise eligible to elect to be treated as a resident alien.

A foreign individual meets the “green card test” if given permission to reside in the U.S. on a permanent basis by U.S. Citizenship and Immigration Services (or a predecessor) and such permission has not been revoked or judicially determined to have been abandoned by the individual.¹

A foreign individual meets the “substantial presence test” if physically present in the U.S. for at least (1) 31 days in 2025 and (2) 183 days during the three-year period that includes 2025, 2024 and 2023, counting only a certain number of days that the individual is present in the U.S. per year, based on the following table:²

Year	Days Counted Toward 183 Day Total
2025	All days present in the U.S.
2024	1/3 of days present in the U.S.
2023	1/6 of days present in the U.S.

In general, an individual is treated as being “physically present” in the U.S. for any day in which he or she is actually present in the U.S. at any time of the day. Despite this, an individual does not count the following as days as being physically present in the U.S.:

(1)     Days that the individual commutes into the U.S. for work from a residence in Canada or Mexico if that individual regularly commutes into the U.S. for work (meaning that the individual commutes on more than 75 percent of workdays during the individual’s working period);

(2)     Days that the individual is in the U.S. for less than 24 hours while in transit between two foreign countries;

(3)     Days that the individual is in the U.S. as a member of a crew of a foreign vessel;

(4)     Days that the individual is only in the U.S. because of a medical condition that arose while in the U.S. and that rendered that individual unable to leave the U.S.; and

(5)     Days that the individual was an exempt individual (including individuals temporarily present in the U.S. as foreign-government related individuals, teachers or trainees on a “J” or “Q” visa, individuals present in the U.S. on a student visa, and certain professional athletes in the U.S. for a charitable sports event).³

A resident alien will be taxed much in the same way as a U.S. citizen, and thus will be subject to U.S. taxation on all worldwide income. Conversely, a nonresident alien will only become subject to U.S. taxation in the event that he engages in certain activities that create a connection between that individual and the United States.