The US is unique on this list: for citizens and green card holders, no day-count test matters at all. For everyone else, the Substantial Presence Test uses a weighted 3-year formula that's easy to miscalculate — which is exactly why we built a dedicated Canada-to-US module into this site's checker tool.
Check My United States Risk →Period: current year days + ⅓ prior year + ⅙ year before, for non-citizens; irrelevant for citizens/green card holders
Add current-year days, plus ⅓ of the prior year's days, plus ⅙ of the year before that. If the total is 183 or more (and you were present 31+ days this year), you're a US tax resident.
US citizens and green card holders are taxed on worldwide income regardless of where they live or how many days they spend anywhere — day count simply doesn't apply to end that obligation.
Holding a Green Card makes you a US tax resident under the Lawful Permanent Resident test, entirely separate from the Substantial Presence Test.
US tax residents owe federal tax on worldwide income at progressive rates up to 37%, plus state tax if domiciled in a taxing state.
The Foreign Earned Income Exclusion (FEIE, Form 2555) lets US citizens abroad 330+ full days in a 12-month period exclude roughly $130,000–$133,000 (2025–2026) of foreign-earned income from federal tax — but annual filing is still required regardless.
A Canadian software contractor works on-site for a US client roughly five months a year on a TN visa: 150 days this year, plus 90 days the year before and 60 days the year before that. Her weighted Substantial Presence Test total is 150 + (90 ÷ 3) + (60 ÷ 6) = 150 + 30 + 10 = 190 — crossing the 183 threshold, which makes her a US tax resident for the year despite never spending more than five months there in any single calendar year. This is precisely the calculation our dedicated Canada→US checker module runs automatically.
Illustrative composite example for educational purposes — not a real individual or filed case.
No — citizens and green card holders are taxed on worldwide income regardless of days present anywhere; the Substantial Presence Test only determines residency status for non-citizens without a green card.
No — it's only available if your current-year days are under 183 and you can demonstrate a closer connection and tax home in another country. If your current-year days alone already exceed 183, you'd instead need to rely on a tax treaty tie-breaker via Form 8833, if a treaty applies.
Yes — Green Card holders are automatically treated as US tax residents under the Lawful Permanent Resident test, independent of any day count or the Substantial Presence Test.
It's a facts-and-circumstances test based on things like where your driver's license, voter registration, and family home are. A cross-border CPA can assess it against IRS criteria before you file Form 8840.
Whatever your risk level, a few concrete steps protect you better than guessing:
This guide is general education only, not tax or legal advice. Rules simplified from public guidance current as of mid-2026 and subject to change — always verify with a licensed tax professional before making decisions. See our full disclaimer.