The US Substantial Presence Test: how the 183-day formula works

Non-US citizens without a green card become US tax residents for a year if they meet the Substantial Presence Test. It’s built around the number 183, but not the way most people expect.

The formula

You meet the test for the current year if you were physically present in the US for:

1. at least 31 days in the current year, and
2. at least 183 days across the current year and the two before it, counting:
   • every day in the current year,
   • one third of the days in the previous year,
   • one sixth of the days in the year before that.

So 120 days a year, every year, adds up to 120 + 40 + 20 = 180: just under. At 122 days a year the total is about 183, and you’d meet the test without ever spending half a year in the US.

What counts as a day

Generally, any day you are physically present in the US for any part of the day counts. There are exclusions, for example for some people in transit between two foreign points, certain commuters from Canada or Mexico, and days you were unable to leave because of a medical condition that arose in the US. Some visa holders, such as certain students, teachers and diplomats, are “exempt individuals” whose days don’t count.

Meeting the test isn’t always the end of it

Even if you meet the test, you may be able to be treated as a non-resident under the closer connection exception (if you were in the US fewer than 183 days in the current year and have a tax home and closer connection to another country), or under a tax treaty tie-breaker. Both have conditions and filing requirements.

Tracking it

Because the formula looks back two years, it’s easy to get surprised in year three. Diego applies the weighted count to your trips and shows your running total, how many days you have left this year before reaching 183, and the date you would cross.

This guide is general information, not tax advice. The US rules include exceptions and elections not covered here; speak to a qualified US tax adviser about your situation.

Common questions

What is the US Substantial Presence Test?

It's the test that makes non-US citizens without a green card US tax residents for a year. You meet it if you were in the US at least 31 days this year and at least 183 days across three years, counting all of this year's days, a third of last year's and a sixth of the year before.

Can I be a US tax resident without spending 183 days in the US?

Yes. Because the formula weights three years, about 122 days a year, every year, is enough to reach 183 weighted days. At 120 days a year the total is 180, just under.

What counts as a day of US presence?

Generally, any day you are physically in the US for any part of the day. Exclusions include some days in transit between two foreign points, certain commuters from Canada or Mexico, and days you couldn't leave because of a medical condition that arose in the US.

Who is exempt from counting days?

Some visa holders, including certain students, teachers and diplomats, are exempt individuals whose days don't count toward the test. Conditions and time limits apply.

Can I meet the test and still be treated as a non-resident?

Possibly. The closer connection exception can apply if you were in the US fewer than 183 days in the current year and have a tax home and closer connection to another country, and a tax treaty tie-breaker may also help. Both have conditions and filing requirements.

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