"As long as I stay under 183 days I'm fine." It's the most common thing snowbirds say, and it's wrong. The real US test is the Substantial Presence Test, which weighs three years of days and can drag you into US tax residency at as few as 121 days a year. There's a way out (the Closer Connection Exception, Form 8840), and a backup if that doesn't work (the treaty tie-breaker). This article walks through how the math actually works and what to file.
You become a US tax resident under the Substantial Presence Test if (a) you spent 31 or more days in the US during the current year, AND (b) the weighted three-year sum is 183 or more days. The weighting: 100% of current year days + 1/3 of prior year + 1/6 of two years ago. So 121 days a year, every year, gets you to exactly 183 - and into US residency.
The IRS treats you as a US resident for tax purposes if you meet both of these:
The threshold sounds high until you actually do the math.
The fix isn't to come down to under 183 weighted days. The fix is the Closer Connection Exception.
If you would otherwise be a US tax resident under the SPT, you can avoid that result by filing Form 8840 and showing that:
This is the form most Canadian snowbirds need to file. It's not a tax return - it's a statement attached to nothing else (or filed separately if no tax return is being filed). Due by the regular tax filing deadline.
Form 8840 asks where the following are located:
For a typical Canadian snowbird, all or nearly all of these point to Canada. The form passes easily.
The Closer Connection Exception is not available if you spent 183 or more days physically in the US during the current year. At that point, you've crossed the line where the IRS won't let you opt out via Form 8840 - even if your life is overwhelmingly in Canada. The fix is then either to take fewer days next year, or to invoke the treaty tie-breaker.
If you spent 183 or more days in the US during the current year, you can't use Form 8840. But you may still be able to be treated as a Canadian resident under the US-Canada treaty Article IV tie-breaker.
To do this, you file:
This is more complex than Form 8840 and triggers professional involvement for most filers. The treaty tie-breaker uses the same sequential test described in our US-Canada Tax Treaty article: permanent home, center of vital interests, habitual abode, citizenship.
Several categories of days are excluded from the SPT count:
For most snowbirds, none of these apply.
This catches a meaningful number of new snowbirds. The form is supposed to be filed every year you would otherwise meet the SPT. If you never file it, the IRS technically can take the position that you were a US tax resident those years, and demand you file Form 1040 reporting worldwide income.
In practice, the IRS rarely enforces this against a clear closer-connection case where the only filing failure is Form 8840. But it can happen, especially if there is unreported US-source income - say, capital gains on US real estate, or US-source business income.
The right defensive posture: file Form 8840 every year you spend more than about 90-100 days in the US, even if you're confident you don't meet the SPT. The paperwork is trivial; the protection it provides is real.
Most snowbirds focus on the US side and assume Canada handles itself. But Canadian residency rules are a separate test from the US SPT - and a snowbird can fail one and not the other.
The rules from the Canadian residency article still apply. If you maintain a primary home, spouse, and significant Canadian ties while spending 5 months a year in Florida, you remain a Canadian tax resident under factual residency. Canada will tax your worldwide income (using foreign tax credits to neutralize US tax on US-source items).
The flip side: if a Canadian snowbird genuinely tries to leave Canada (sells the Toronto house, severs ties), but spends 200 days in the US, they're potentially a US resident under SPT, no longer a Canadian resident under domestic Canadian law, and the treaty tie-breaker may not save them - because they may not have a "permanent home" or "center of vital interests" clearly in either country anymore.
Falling out of Canadian residency without becoming clearly resident in any country, while still meeting the US SPT. Result: the US treats you as a worldwide-income resident; Canada treats you as a non-resident; you have lost the treaty's clear residence answer; and you owe US tax on income you previously didn't think the US could touch. The way to avoid this: don't half-leave Canada. Either commit to leaving (and document the move), or stay a Canadian resident and use Form 8840 / Article IV to stay out of US residency.
Buying a Florida (or Arizona, or California) winter home is the moment many Canadian retirees first encounter cross-border tax complexity. Things to know:
Track your days carefully. Every year. Not just for the current year - the SPT is three-year weighted, so prior-year counts matter for years to come. CBP entry/exit data is the IRS's source of truth in any dispute.
File Form 8840 every year you spend more than 90 days in the US. The form is two pages and takes 20 minutes. It builds a record.
Don't blow through 122 days carelessly. Aim for under 120 days a year as a routine, with 122 as the point where Form 8840 becomes mandatory in practice.
If a particular year exceeds 183 US days, plan ahead. The treaty position via Form 1040-NR + Form 8833 is the right answer, but it requires actual analysis of the tie-breaker tests. Don't try this DIY for a year with significant US presence.
Reconcile US and Canadian residency every year. Don't assume that "I'm Canadian" is enough on the Canadian side - if you've stripped your Canadian ties, you may have left without realizing it. And don't assume "I'm not a US resident" is enough on the US side without filing Form 8840.