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 for five calendar years), teachers and trainees on J or Q visas (generally two of the last six years), foreign government-related individuals on A or G visas, and professional athletes at charitable events. You 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.
• 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 you have applied for a green card.
• 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 (from your residency starting date — usually 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 from the day the card is issued regardless of days, so the test matters mainly for visitors, B-visa holders, 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