What is the substantial presence test?

The formula

You are a US resident alien for a calendar year if both of these are true:

1. 1You were physically present in the US on at least 31 days during the current year, and
2. 2Your weighted total is at least 183 days: every day this year + 1/3 of your days last year + 1/6 of your days the year before.

Example: 120 days in each of the last three years gives 120 + 40 + 20 = 180 — under the line. 122 days a year gives 122 + 40.67 + 20.33 = 183 — resident. That is why the safe long-run average is often quoted as “121 days a year.” The substantial presence test calculator runs the weighted sum from your trip dates and shows how many more days you can spend this year.

Which days count

Any part of a day in the US counts as a full day — arrival and departure days included. The IRS then excludes certain days entirely:

• Exempt individuals — students on F, J, M or Q visas (generally not after five calendar years as an exempt individual), teachers and trainees on J or Q visas (not if you were already exempt as a teacher, trainee or student in any part of two of the six preceding calendar years), foreign government-related individuals on A or G visas (other than A-3 and G-5), and professional athletes at charitable sports events. Everyone in these groups except foreign government-related individuals must file Form 8843 to claim the exclusion.
• Medical condition — days you could not leave because of a condition that arose while you were in the US. This exclusion is also claimed on Form 8843.
• Regular commuters from Canada or Mexico on more than 75% of workdays.
• Transit of under 24 hours between two foreign points, and days as a crew member of a foreign vessel.

Meeting the test but staying non-resident

Two escape routes exist even after you cross 183 weighted days:

• Closer connection exception — if you were in the US fewer than 183 actual days this year, keep a tax home in a foreign country, and have a closer connection to it than to the US, you can file Form 8840 and remain a non-resident. It is not available if during the year you applied for, or took other steps toward, a green card, or had an application for adjustment of status pending.
• Treaty tie-breaker — if you are also resident of a treaty country under its law, the treaty’s Article 4 tests (permanent home, centre of vital interests, habitual abode, nationality) can assign you to that country. Claim it on Form 8833; you still file in the US as a non-resident. See dual residence.

What happens if you meet it

You are taxed like a US citizen on worldwide income for the year (in your first year of residence, from your residency starting date — generally your first day of presence that year), file Form 1040 rather than 1040-NR, and pick up US reporting duties such as FBAR and FATCA for foreign accounts. Green card holders are resident under a separate test regardless of days (from the first day they are in the US as a lawful permanent resident), so the test matters for every other non-citizen — visa workers, long-stay visitors, and people between statuses. The full rule, with edge cases and a worked example, is in the US Substantial Presence Test rule.

Sources

• IRS — Substantial Presence Test
• IRS — Publication 519, U.S. Tax Guide for Aliens
• IRS — Form 8843, Statement for Exempt Individuals