Country guideTax residency
Tax residency in the United States: how the day count works
The United States decides tax residency for non-citizens with the Substantial Presence Test: you must be present at least 31 days in the current year, and your weighted three-year total must reach 183 days. The formula counts all days this year, one third of last year's days and one sixth of the year before. It is not a simple 183-days-per-year rule.
What is the day threshold in the USA?
For non-citizens without a green card, the IRS Substantial Presence Test decides residency, and it works differently from every simple day rule. You are a US tax resident for a year if you were present at least 31 days during that year, and your weighted total reaches 183: all days in the current year, plus one third of your days in the prior year, plus one sixth of your days in the year before that.
The weighting is the trap. Regular visitors accumulate residue from past years, so a pattern that never touches 183 real days in any year can still cross the weighted line. Green-card holders are resident by status alone, whatever their day count.
| Day threshold | 183 weighted days over 3 years, plus 31 actual days in the current year |
|---|---|
| Counting window | Calendar year, with 1/3 and 1/6 weights on the two prior years |
| Partial days | Any part of a day counts, with listed exceptions such as transit under 24 hours |
| Other triggers | Green card test; residency by status regardless of days |
| Source | IRS |
Calendar year or rolling window?
Calendar years, three of them at once. Each year stands alone for the 31-day minimum and contributes to the weighted sum: the current year at full value, the prior year at one third, the year before at one sixth. The practical rule of thumb that falls out of the arithmetic: a steady 120 days per year keeps the weighted total at 180, just under the line, while 122 a year puts you at 183 exactly. One heavy year takes two further years to wash out of the formula.
Do partial days count?
Yes, as a default: you are treated as present on any day you are physically in the United States at any time. The IRS then lists specific exceptions. Days in transit between two foreign points for less than 24 hours, days commuting to US work from a residence in Canada or Mexico on a regular schedule, days as crew of a foreign vessel, days you could not leave because of a medical condition that arose in the US, and days as an exempt individual, which covers students on F and J visas and certain teachers and trainees for limited years.
What else can make you resident besides days?
Status. The green card test makes lawful permanent residents US tax residents from their first day in that status, with no day counting at all. In the other direction, meeting the Substantial Presence Test does not always end the matter: the closer-connection exception can preserve non-resident status if you spent fewer than 183 actual days in the current year, maintain a tax home in another country and file Form 8840 on time. Treaty tie-breakers can also override the domestic result. And remember that US states run their own residency rules on top, with their own day counts.
A worked example with 2026 dates
130 days in 2026, resident by formula
A Canadian consultant spends 10 March to 20 May and 1 September to 28 October 2026 in the US, 130 days in total, after 120 days in each of 2025 and 2024.
| Year | Days present | Weight | Counted |
|---|---|---|---|
| 2026 | 130 | x 1 | 130 |
| 2025 | 120 | x 1/3 | 40 |
| 2024 | 120 | x 1/6 | 20 |
| Total | 190 of 183 |
He was present well over 31 days in 2026 and his weighted total is 190, so he meets the test and is a US tax resident for 2026, despite never exceeding 130 actual days in any year. Because his 2026 actual days are under 183, he can still claim the closer-connection exception with Form 8840 if his tax home stayed in Canada.
How do I track my days for the USA?
You need three years of day counts, not one, and the formula is fiddly enough to get wrong by hand. Run your actual numbers, then re-run them before booking each additional trip.
Run the three-year formula
The free Substantial Presence Test calculator applies the exact IRS weighting to your day counts for 2024 through 2026.
Three years of days, kept straight
Staydays logs your US days automatically, year after year, so the weighted formula always has accurate inputs.
Frequently asked questions
Is the US rule just 183 days in a year?
No. The Substantial Presence Test needs two things: at least 31 days of presence in the current year, and a weighted total of 183 across three years, counting all of this year, one third of last year and one sixth of the year before. You can meet it without ever spending 183 actual days in any single year.
How many days per year keep me under the test long-term?
About 120. If you spend the same number of days every year, the formula gives that number times 1.5, and 121 times 1.5 is 181.5, just under the line. At 122 days a year the weighted total reaches 183 and you meet the test.
Which days do not count toward the test?
Days as an exempt individual, such as students on F or J visas and teachers or trainees for limited years, days you commute from Canada or Mexico on a regular schedule, days in transit for under 24 hours, days as crew of a foreign vessel, and days you could not leave because of a medical condition that arose in the US.
What if I meet the test but really live in another country?
Two outs exist. The closer-connection exception applies if you were under 183 actual days in the current year, keep a tax home in another country and file Form 8840. Failing that, a double-tax treaty tie-breaker can still assign your residency to the other country.
This guide is general information, not legal or tax advice. Rules change and individual circumstances differ. Confirm details with official sources or a qualified advisor.
Last updated: 2026-07-14