United States — Substantial Presence Test

Summary

Threshold

183 weighted days

Window

3 calendar years

Also required

31+ days in the current year

Effect

Worldwide income taxed

Authority

IRS (Internal Revenue Code)

A non-citizen becomes a US tax resident for a calendar year if they meet the IRS Substantial Presence Test. You meet it if you were physically present in the United States for at least 31 days during the current year and for 183 weighted days across the current year plus the two years before it — where days in earlier years count for less. Meeting the test means the US taxes your worldwide income, and it applies by day count alone, regardless of your visa or immigration status.

Who it applies to

This matters most if you are:

• A non-US citizen who is not already a lawful permanent resident (green-card holder).
• A frequent business traveler, remote worker, or digital nomad spending long stretches in the US.
• Someone with a US property, family, or work pattern that adds up to a lot of days over several years.

It applies to individuals regardless of nationality. Green-card holders are already US tax residents under a separate test, so the Substantial Presence Test is chiefly about people without permanent residency.

The rule — and why it exists

You meet the Substantial Presence Test for the current year if both conditions are true:

• 31-day floor. You were present in the US for at least 31 days during the current calendar year, and
• 183 weighted days. Your weighted day total over the current year and the two prior years reaches or exceeds 183, using the 1, 1/3, 1/6 weighting.

Why it exists: the US uses physical presence as a proxy for where someone genuinely lives and earns. Weighting recent years more heavily captures people who are effectively based in the US over time, while still exempting the occasional short visitor. Because it is objective and day-based, it removes the guesswork of judging intent — but it also means someone can trip into full US tax residency without ever intending to move there.

Counting the days

Days across the three years are not counted equally. Add up your US days for each year with these weights:

1. 1All of the days you were present in the current year (× 1), plus
2. 2One-third (1/3) of the days you were present in the first prior year, plus
3. 3One-sixth (1/6) of the days you were present in the second prior year.

If the weighted total reaches or exceeds 183 — and you had at least 31 days in the current year — you meet the test. Any part of a day physically present in the US generally counts as a full day, including arrival and departure days, unless a specific exclusion applies (see below).

Examples

Example 1 — just under the line

You spend 120 US days in each of the three years. The weighted total is 120 × 1 = 120, plus 120 × 1/3 = 40, plus 120 × 1/6 = 20, for 180 weighted days — just under 183, so you do not meet the test.

Example 2 — a single heavy year

You were rarely in the US before, but this year you spend 200 days there. That alone is 200 weighted days — above 183 and well above the 31-day floor — so you meet the test for the current year regardless of the prior two years.

Example 3 — tipping over on the weighting

You spend about 122 days in the US each year. That is 122 + (122 × 1/3 ≈ 41) + (122 × 1/6 ≈ 20) ≈ 183 weighted days — right on the threshold, so you meet the test even though no single year hit 183 actual days.

Exceptions & edge cases

Not every day of physical presence is a "day in the US." The IRS excludes, among others:

• Days you regularly commute to work in the US from a residence in Canada or Mexico.
• Days you are in the US for less than 24 hours while in transit between two foreign points.
• Days you are unable to leave because of a medical condition that arose while you were in the US.
• Days as an "exempt individual" — including certain students (F, J, M, Q visas), teachers and trainees, foreign-government-related individuals, and professional athletes competing in a charity event.

Two further routes can undo residency even if you pass on the numbers:

• Closer Connection Exception. If you were in the US fewer than 183 days in the current year, kept a tax home abroad, and have a closer connection to a foreign country, you can be treated as a nonresident by filing Form 8840.
• Tax treaties. A double-taxation treaty tie-breaker can reassign residency to your home country even when you meet the domestic test.

Common misconceptions

• "183 means 183 days in one year." No — it's a weighted total across three years, so far fewer than 183 actual days can still trigger it.
• "My visa protects me." The test is independent of immigration status; a nonimmigrant can become a US tax resident by day count alone.
• "Only my US income is taxed." Residency brings worldwide income into scope, subject to treaties and foreign tax credits.
• "Arrival and departure days are free." Any part of a day present in the US generally counts as a full day unless a specific exclusion applies.

Frequently asked questions

Sources

• IRS — Substantial Presence Test
• IRS — Closer Connection Exception to the Substantial Presence Test