The United States decides tax residency by counting days: a green card, or the substantial presence test (31 days this year plus a weighted 183-day total across three years), makes you a US tax resident on worldwide income. Canada decides by ties: a dwelling, a spouse or common-law partner, or dependants in Canada makes you a factual resident regardless of days spent there, and 183 days of sojourning makes you a deemed resident without them. When both countries claim the same person, Article IV of the treaty breaks the tie.
The two systems fail in opposite directions. The US test is pure arithmetic, so it catches snowbirds who never spent close to 183 days in any single year. The Canadian test is qualitative, so it holds on to departing Canadians long after they think they left. CrossingHQ’s working rule: any Canadian who winters in the US should know their three-year day total each January, and file Form 8840 by the June deadline the year the total crosses 183. That one page of paper separates a snowbird with a US vacation habit from an accidental US tax resident filing on both sides of the border.
How the US decides: two tests, either one catches you
US tax residency for a non-citizen runs through two independent tests; meeting either makes you a US tax resident for that calendar year.[IRS, Determining an Individual's Tax Residency Status, 2026-07]
The green card test
A lawful permanent resident of the United States is a US tax resident. Days do not matter: a green-card holder who lives full-time in Toronto and has not entered the US in years still meets the test. Residency continues until the card is formally abandoned or revoked, not merely allowed to gather dust. Long-term holders who give it up can also face the expatriation regime, one reason the card is a poor souvenir.
The substantial presence test
The substantial presence test is a formula. You are a US tax resident for the current year if you were physically present in the US on at least 31 days that year, and your weighted three-year total reaches 183. The weighting counts every day of the current year, one-third of the prior year’s days, and one-sixth of the year before that.[IRS, Substantial Presence Test, 2026-07]
The weighting is what surprises snowbirds: a Canadian who spends 130 days in Florida every winter never comes near 183 in any single year, but the weighted math reads 130 + 43 + 22 = 195. Test met. A steady pattern breaks even at about 121 days per year (121 + 40 + 20 = 181); anything above that trips the formula by year three.
Some days do not count: regular commuting days to US work from a Canadian residence, days under 24 hours in transit between two non-US points, 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 (certain students, teachers, trainees, and foreign-government personnel).[IRS, Substantial Presence Test — days of presence exclusions, 2026-07] Everything else counts, and a partial day is a full day: land at Buffalo at 11 p.m. and that day is on the tally.
The closer connection exception: Form 8840
A snowbird who was present in the US fewer than 183 actual days in the current year, maintained a tax home in Canada for the entire year, and kept a closer connection to Canada than to the US can file Form 8840, the Closer Connection Exception Statement, and be treated as a nonresident despite the formula.[IRS, Closer Connection Exception to the Substantial Presence Test, 2026-07]
Closer connection is measured on facts: where the permanent home is, where family lives, where the driver’s licence and voter registration sit, where banking and business run. For the typical Ontario or BC snowbird with a house, a spouse, provincial health coverage, and accounts at home, the test is easy to meet. The filing is the hard part: Form 8840 attaches to a Form 1040-NR if one is filed, or is mailed alone by the 1040-NR due date, which for a snowbird with no US wages is June 15. Miss the deadline and the exception is lost for that year unless the IRS accepts you made reasonable, documented attempts to comply.
Two disqualifiers close the door. Spend 183 or more actual days in the US in the current year and the exception is unavailable, no matter how Canadian your life is; the only relief left is the treaty. Apply for a green card, or have an adjustment-of-status application pending that year, and the exception is off the table too.[IRS, Closer Connection Exception — Form 8840 requirement and disqualifications, 2026-07]
How Canada decides: ties first, then a day count
Canada has no statutory formula for ordinary residency. The Canada Revenue Agency determines factual residency from the whole picture of a person’s residential ties, under the framework in Income Tax Folio S5-F1-C1.[CRA, Income Tax Folio S5-F1-C1: Determining an Individual's Residence Status, 2026-07]
Factual residency: significant and secondary ties
Three ties carry almost all the weight. A dwelling in Canada that remains available for your occupation, a spouse or common-law partner, and dependants in Canada are each a significant residential tie. Keep any of them and the CRA will treat you as a factual resident of Canada, taxable on worldwide income, however many days you spent abroad.[CRA, Folio S5-F1-C1 — significant residential ties, 2026-07]
Secondary ties fill in when the significant ones are ambiguous: personal property, provincial health coverage, a Canadian driver’s licence, bank accounts and credit cards, social and professional memberships. No single secondary tie decides anything, but a cluster of them does. This is why “I moved to Arizona” is not a tax event while “I sold the Toronto house, my spouse came with me, and I cancelled OHIP” is. The CRA gives advance opinions on residency through Form NR73 (leaving Canada) or NR74 (entering); filing one is optional, and many cross-border advisors prefer to document the facts without inviting a ruling.
Deemed residency: the 183-day sojourner rule
The Income Tax Act also deems a person resident for the whole year if they sojourned in Canada 183 days or more in a calendar year, under paragraph 250(1)(a).[Income Tax Act, paragraph 250(1)(a) — deemed resident, sojourning 183 days or more, 2026-07] Sojourning means a temporary stay rather than settled living, which is what an American snowbird does in a Muskoka cottage. This rule is how a US retiree who overstays a Canadian summer becomes taxable in Canada for the entire year, not just the months present.
The two systems side by side
| United States | Canada | |
|---|---|---|
| Primary test | Day-count formula (substantial presence) or green card | Residential ties (factual residency) |
| Statutory day rule | 31 days current year plus weighted 183 over three years | 183 days sojourning in one calendar year |
| Ties-based test | Only as an exception (closer connection) | The main test |
| Escape hatch | Form 8840, or treaty Article IV | Treaty Article IV, then deemed non-residency |
| Cost of residency | Worldwide income tax plus foreign-account reporting | Worldwide income tax, provincial tax, foreign-property reporting |
| Cost of exit | Expatriation rules for long-term green-card holders | Departure tax deemed disposition |
A Canadian can control the US outcome with a calendar and a filing habit. Controlling the Canadian outcome requires changing facts on the ground: the house, the spouse’s location, the health card. Day counting alone never ends Canadian factual residency.
The Article IV tie-breaker: when both countries say yes
Dual residency is common at the edges: the snowbird who blew past 183 actual US days while the family home sat in Ottawa, or the executive with a green card and a Vancouver house. The Canada-US Convention, signed in 1980 and amended by protocols through 2007, exists for this collision.[IRS, Canada Tax Treaty Documents (1980 Convention and Protocols), 2026-07] This page covers the tie-breaker as it bears on residency; the full treaty mechanics, article by article, are in the Canada-US tax treaty guide, and the general architecture every treaty shares is in how tax treaties work.
Article IV(2) resolves it with a cascade, applied in order, stopping at the first test that gives an answer.[Finance Canada, Convention Between Canada and the United States of America With Respect to Taxes on Income and on Capital, Article IV, 2026-07]
- Permanent home. Resident of the country where a permanent home is available. A home in both countries, or neither, moves to the next test.
- Centre of vital interests. Resident of the country where personal and economic relations are closer: family, employment, investments, community.
- Habitual abode. Resident of the country where the person habitually lives, in practice where more time is spent.
- Citizenship. Resident of the country of citizenship.
- Competent authority. If citizenship does not settle it (dual citizens, or citizens of neither), the tax authorities decide by mutual agreement.
A worked snowbird example
Take a retired couple from London, Ontario who spent 200 days in the US one year: a long winter in Naples, Florida plus a spring health scare that delayed the drive home. At 200 actual days, the substantial presence test is met and Form 8840 is unavailable. The US claims them. Canada claims them too, since their house, accounts, and provincial coverage never moved. Dual residents for the year.
Article IV sorts it in one step for most such couples. They own the London house year-round; the Naples condo is a January-to-April rental. A permanent home is available only in Canada, so the treaty deems them Canadian residents, and the US must treat them as nonresidents for treaty purposes. They file a US nonresident return with Form 8833, the treaty-position disclosure, report worldwide income to the CRA as usual, and the year closes without double taxation. Now change one fact: they bought the condo and kept it available all year. A permanent home exists in both countries, and the analysis drops to centre of vital interests, where their Ontario family, accounts, and history still win, but now as a facts-and-circumstances argument, not a clean answer.
The exit consequence Canadians miss
Winning the tie-breaker for the other side has a price. When the treaty assigns a factual Canadian resident to the US, subsection 250(5) of the Income Tax Act deems that person a non-resident of Canada.[Income Tax Act, subsection 250(5) — deemed non-resident under a tax treaty, 2026-07] That is an emigration event, triggering the departure-tax deemed disposition of most capital property at fair market value, the same as physically leaving. A snowbird who buys the Florida house, sells the Canadian one, and drifts across the treaty line can realize the departure tax without booking a moving truck. The mechanics are in the departure tax guide.
What accidental dual residency costs
Managed, this is routine paperwork. Unmanaged, the failures look like this:
The missed 8840. A snowbird trips the weighted formula, files nothing, and is a US tax resident by default: worldwide income reporting to the IRS plus the foreign-account disclosure stack (FBAR and related forms) on every Canadian account, with penalties that dwarf any tax owing. The income tax usually resolves through foreign tax credits; the information-return penalties do not.
The lingering green card. A former US permanent resident moves home to Canada and assumes the card expired into irrelevance. The IRS does not agree, and years of unfiled US resident returns accumulate. Claiming treaty non-residence is possible but carries immigration consequences for a green-card holder and can start the expatriation clock.
The half-departure from Canada. Someone declares non-residency to the CRA while a spouse stays in the Canadian house. The significant tie stands, the claim fails on review, and the CRA reassesses years of worldwide income, including never-reported foreign rental income and property gains. The rules for foreign rental income and the T1135 disclosure apply for every year the person was in fact resident.
Who is fine: the snowbird who counts days and files the 8840 annually, and the emigrant who makes a clean break: ties severed, departure return filed. Who loses: anyone running a residency position by feel, especially with a home available in both countries.
FAQ
Can I be a tax resident of Canada and the US in the same year?
Yes, under each country’s domestic law, and it happens routinely. The treaty tie-breaker then assigns a single residence for treaty purposes. The assignment is claimed on the relevant filings, not automatic, and both countries’ paperwork still gets done for the year.
Does filing Form 8840 mean I owe US tax?
No. Form 8840 is a statement, not a return. It tells the IRS your tax home and closer connection stayed in Canada despite the formula, so it should treat you as a nonresident. A snowbird with no US-source income who files on time typically owes nothing and files nothing else.
How many days can a snowbird spend in the US without becoming a tax resident?
About 121 days per year keeps a steady pattern’s weighted three-year total under 183. Above that, Form 8840 becomes the annual safeguard, and it works until actual presence in a single year hits 183; past that, only the treaty restores nonresident treatment. Immigration day limits are a separate regime with different math; satisfying one does not satisfy the other.
Does keeping a Canadian bank account make me a Canadian tax resident?
Not by itself. A bank account is a secondary tie, and secondary ties matter in clusters. The ties that decide cases are the significant three: an available dwelling, a spouse or partner, and dependants in Canada.
Where this fits in the library
This page covers how residency is decided. What it costs is spread across the tax library: the departure tax deemed disposition for Canadians who cease residency, the T1135 foreign-property disclosure and foreign rental income rules for Canadians who stay resident while owning abroad, and estate planning across the border for property that will outlive the plan. For the full Canadian owner’s framework, start with buying property abroad as a Canadian.
Disclaimer
This article is for informational purposes only and does not constitute tax advice. Tax laws change frequently and individual circumstances vary. Residency determinations are fact-specific, and the stakes of getting one wrong span both countries’ filing regimes. Consult a qualified cross-border tax advisor before making decisions based on this information. CrossingHQ does not provide tax preparation, advice, or representation services.
Current as of 2026-07-23. We review tax content quarterly and update on rule changes. To report an error, contact us.