Part I—Explanation of Status—Resident or Nonresident Alien

Generally, you are considered a resident alien if you meet either the green card test or the substantial presence test for 2026. You are considered a nonresident alien for the year if you do not meet either of these tests. For more information on resident and nonresident alien status, see Pub. 519 .

Green card test. You are a resident alien for tax purposes if you are a lawful permanent resident of the

Days of presence in the United States. Generally, you are treated as present in the United States on any day that you are physically present in the country at any time during the day. However, you do not count the following days of presence in the United States for the substantial presence test.

• Days you commuted to work in the United States from a residence in Canada or Mexico if you regularly commuted from Canada or Mexico.

• Days you were in the United States for less than 24 hours while you were traveling between two places outside the United States.

• Days you were temporarily present in the United States as a regular member of the crew of a foreign vessel engaged in transportation between the United States and a foreign country or a territory of the United States. This rule does not apply to any day you were otherwise engaged in a trade or business in the United States.

• Days you intended, but were unable, to leave the United States because of a medical condition or medical problem that arose while you were in the United States.

• Days you are in the United States under a NATO visa as a member of a force or civilian component to NATO. However, this exception does not apply to an immediate family member who is present in the United States under a NATO visa. A dependent family member must count

Instructions for Form 1040-C (Rev. 1-2026) 5

every day of presence for purposes of the substantial presence test.

• Days you were an exempt individual. In general, an exempt individual is (a) a foreign government-related individual, (b) a teacher or trainee, (c) a student, or (d) a professional athlete who is temporarily present in the United States to compete in a charitable sports event.

If you qualify to exclude days of presence in the