The two tests that decide it
If you are not a U.S. citizen, the IRS treats you as a non-resident alien unless you meet one of two tests.Pub. 519
- The green card test. You are a lawful permanent resident of the U.S. at any time during the calendar year.Pub. 519
- The substantial presence test. You were physically in the U.S. at least 31 days this year and at least 183 days over the three-year period, counting all days this year, one third of the days last year and one sixth of the days the year before.Pub. 519
Meet either one and you are a resident alien for that year. Meet neither and you are a non-resident alien.Pub. 519
How the day count works
Take a person who spent 120 days in the U.S. in each of three years. The IRS counts 120 days for this year, 40 for last year (a third of 120) and 20 for the year before (a sixth of 120). That totals 180, under 183, so they do not pass the substantial presence test.Pub. 519
Some days do not count at all. These include days you commute to work from a home in Canada or Mexico, days in transit for less than 24 hours between two places outside the U.S., days you could not leave because of a medical condition that began while you were here, and days you are an "exempt individual", such as certain teachers, trainees and students on J, Q, F or M visas.Pub. 519
Exempt individual does not mean exempt from tax. It is the IRS label for people whose days are not counted.Pub. 519
Which form for which situation
| Your situation | Form | Why |
|---|---|---|
| U.S. citizen, anywhere | Form 1040 | Citizens file as residents. A citizen does not need an ITIN.IRS |
| Green card holder | Form 1040 | You pass the green card test, unless a treaty tie-breaker applies.Pub. 519 |
| Passes the substantial presence test | Form 1040 | You are a resident alien for the year.Pub. 519 |
| Fewer than 31 days in the U.S., or under 183 weighted days | Form 1040-NR | You are a non-resident alien if you pass neither test.Pub. 519 |
| Passes the day count but has a closer connection to another country | Form 1040-NR | Possible if you were here under 183 days, kept a tax home abroad and file Form 8840 by the due date.Pub. 519 |
| Dual resident covered by a treaty tie-breaker | Form 1040-NR with Form 8833 | You can be treated as a non-resident if the treaty says your home country wins.IRS |
| Arrived or left the U.S. during the year | Special rules (dual-status) | You can be a non-resident and a resident in the same year.Pub. 519 |
| Non-resident married to a U.S. citizen or resident | Form 1040-NR, or a joint Form 1040 | You can choose to be treated as a resident and file jointly if you meet the conditions.Pub. 519 |
Our non-resident guide gives more examples, and the Form 1040-NR guide shows how the non-resident return works.
Which form needs an ITIN?
Either form needs a taxpayer number. A non-resident who is not eligible for an SSN and has to file Form 1040-NR applies for an ITIN, and the return goes in with Form W-7.IRS The same goes for a resident alien who is not eligible for an SSN.IRS See our ITIN service, or have us prepare the return with the 1040-NR service. This is general information, not tax advice.
Your questions answered
Form 1040-NR if you are a non-resident alien. Form 1040 if you are a citizen or a resident alien, meaning you hold a green card or pass the substantial presence test.Pub. 519
At least 31 days in the U.S. this year and at least 183 days over three years, counting this year in full, one third of last year and one sixth of the year before.Pub. 519
If it was 120 days in each of three years, the weighted total is 180 and you do not pass the test, so you are a non-resident.Pub. 519 Other facts can change that, so check your own day counts.
Only in narrow cases, such as a dual resident who relies on a treaty tie-breaker and files Form 8833 with Form 1040-NR.IRS
No. A U.S. citizen is eligible for an SSN, and an ITIN is only for people who are not.IRS
More questions? See the full Nolly.com FAQ.
How we checked this
Every IRS fact on this page comes from IRS.gov or the other official pages listed below and was checked on October 2, 2026. Nolly.com's own prices are the only exception. Nolly.com is a private company and is not part of the IRS.
Nolly Services Inc, d/b/a Nolly.com, appears on the IRS page Acceptance agents – Canada. Nolly.com is a private company and isn't part of the IRS.
- Instructions for Form W-7 (Rev. 12-2024)https://www.irs.gov/instructions/iw7
- Individual Taxpayer Identification Number (ITIN)https://www.irs.gov/individuals/individual-taxpayer-identification-number
- Publication 519, U.S. Tax Guide for Alienshttps://www.irs.gov/publications/p519
- Instructions for Form 1040-NR (2025)https://www.irs.gov/instructions/i1040nr
- Instructions for Form 8840https://www.irs.gov/instructions/i8840
Checked against IRS.gov on October 2, 2026. General information, not tax advice.
