A nonresident alien is an individual who is neither a US citizen nor a resident alien for US federal income tax purposes, meaning the person is not a lawful permanent resident, does not meet the substantial presence test, and has not made the first-year election. The Internal Revenue Code says it in those terms: an individual is a nonresident alien if such individual is neither a citizen of the United States nor a resident of the United States within the meaning of subparagraph (A) (26 U.S.C. 7701(b)(1)(B)). Alien is the Code’s own word for an individual who is not a US citizen (IRS, Topic no. 851).
How the Status Is Determined
The definition is a negative, so the work sits in the residency test. An alien individual is treated as a resident of the United States for a calendar year if, and only if, the individual is a lawful permanent resident at any time during that year, meets the substantial presence test, or makes the first-year election (26 U.S.C. 7701(b)(1)(A)). The first clause is the green card test, the second is the day count, and the third is an election rather than a test of facts.
Any single clause makes the person a resident alien, so nonresident status requires that none of them is satisfied. Someone who falls well short on days but holds a green card is still a resident alien.
The Substantial Presence Day Count
Both prongs have to be met. The individual must be present in the United States on at least 31 days during the current calendar year, and the sum of the days present in the current year and the 2 preceding calendar years, each multiplied by the applicable multiplier, must equal or exceed 183 days (26 U.S.C. 7701(b)(3)(A)).
The count is weighted rather than a running total. Days in the current year count in full, days in the first preceding year count as 1/3 of the days present, and days in the second preceding year count as 1/6 (IRS, Substantial presence test).
Some days never enter it. An individual is not treated as present on any day the individual is an exempt individual, which the Code defines as a foreign government-related individual, a teacher or trainee, a student, or a professional athlete competing in a qualifying charitable event, or on any day the individual was unable to leave the United States because of a medical condition that arose while the individual was present here (26 U.S.C. 7701(b)(3)(D) and (b)(5)). Clearing the weighted total does not always settle it either, because someone present on fewer than 183 days in the current year who establishes a tax home and a closer connection abroad is not treated as meeting the test (26 U.S.C. 7701(b)(3)(B)).
A Worked Day Count
Say an individual was present in the United States on the days below, holds no green card, made no election, and is not an exempt individual.
stated inputs, days physically present
current year 90
first preceding year 180
second preceding year 180
raw days across the three years 450
weighted count
current year, counted in full 90
first preceding year, 1/3 of 180 60
second preceding year, 1/6 of 180 30
weighted total 180
31-day prong met, 90 is at least 31
183-day prong not met, 180 is under 183
result nonresident alien for the current yearOnly the current year counts in full, so a person can spend real time in the country across two earlier years and still land outside the test. Three more days of presence in the current year would carry the weighted total to the threshold and make the same person a resident alien.
What the Status Changes in a Firm’s Work
A nonresident alien engaged in a trade or business in the United States during the year must file a US income tax return and report all income from US sources (IRS, Topic no. 851), and that return is Form 1040-NR, U.S. Nonresident Alien Income Tax Return, rather than Form 1040 (IRS, About Form 1040-NR).
The trade or business is not the only trigger. A nonresident alien not engaged in a US trade or business still files Form 1040-NR with Schedule NEC where the amount of tax withheld on US source income did not fully satisfy the tax due, or where a refund of overwithheld or overpaid tax is claimed (IRS, Topic no. 851).
The IRS guide that collects the status rules is Publication 519, U.S. Tax Guide for Aliens, currently the 2025 revision (IRS, Publication 519).
The status reaches past the individual return. It is what a foreign individual certifies to a payer on Form W-8BEN, which a beneficial owner must give to the withholding agent or payer when that owner is a nonresident alien (IRS, Instructions for Form W-8BEN), and that certification is worked through in offshore contractor misclassification risk. The status is also the shareholder disqualifier for S corporation stock (26 U.S.C. 1361(b)(1)(C)), covered with the rest of the eligibility list in C corp vs S corp.
What It Is Commonly Confused With
Resident alien for tax purposes. The same individual on the other side of the same tests, decided for each calendar year, so one person can be a nonresident alien in one year and a resident alien in the next (IRS, Topic no. 851).
Immigration status. The green card test turns on lawful permanent residence under the immigration laws, but the day count turns only on physical presence, so a visa category does not by itself settle the tax answer (IRS, Topic no. 851).
Dual-status year. One tax year in which the status changes from resident alien to nonresident alien or the other way round, usually the year the person arrives in or departs from the United States (IRS, Topic no. 851).
Common Questions
Any individual who is neither a US citizen nor a resident alien for the period in question (IRS, Topic no. 851). The period matters, because the answer can change from one calendar year to the next.
Test the residency clauses in turn: lawful permanent resident status on any day of the calendar year, then the weighted day count, then a first-year election. If none applies, the person is a nonresident alien for that year (26 U.S.C. 7701(b)(1)).
A short-stay business visitor with no green card, because too few days accumulate. A student temporarily present under a qualifying visa can land there too, because those days of presence are not counted while the exemption applies (26 U.S.C. 7701(b)(3)(D) and (b)(5)).
The student exemption runs out. For any calendar year after the 5th calendar year in which the individual was an exempt individual as a teacher, trainee or student, the student exemption stops applying unless the individual establishes both an intent not to reside permanently in the United States and substantial compliance with the requirements for being present under the visa (26 U.S.C. 7701(b)(5)(E)(ii)).
Citizenship, and little else about how the income is taxed. A resident alien follows the same tax laws that apply to US citizens, reports worldwide income, and files Form 1040 (IRS, Topic no. 851).
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