How do I work out how many US days I actually had?
From records, not memory. Start with entry and exit dates for the whole look-back period rather than the current year, because the count weights this year most heavily and then adds fractions of the two before it. Passport stamps, border crossing histories, flight itineraries, card activity and the dates a car insurance policy was switched all help pin down arrivals and departures. Count the whole period before drawing any conclusion. The most common error we correct is a count built from a single winter, which is a different and much smaller number than the one the test actually uses.
Which travel records should a snowbird be keeping?
A simple dated list of every arrival and departure, kept as the year goes, beats anything reconstructed afterwards. Keep the boarding passes or the border crossing record behind it, and note the year each entry belongs to rather than the season, because a winter straddles two of them. Keep the evidence of where your life is based as well: the Canadian home, the family, the licence and registrations, the accounts. If the count is met, that second set of facts is what supports the position that your tax home stayed in Canada, and it is far easier to assemble now than years later.
When in the year should I decide whether I am a US tax resident?
Before the winter, not after it. The count is arithmetic you can run in advance, so the decision about how long to stay can be taken with the consequence known. Once the season is over the arithmetic is fixed and the only remaining question is which filing to make. There is a second reason for deciding early: the facts that support a Canadian tax home are easier to keep than to recover, and some of the things people do while in the US — a local licence, a registered car, a homestead claim — make one of the two routes out harder to argue.
My count is met this year — what happens next?
You choose between two positions, and each of them is a filing. If your tax home and the centre of your life stayed in Canada, the statement to that effect is the ordinary route and the facts behind it are the work. If the US facts are strong enough that it will treat you as resident regardless, the treaty tie-breaker is the route instead, and that is a different filing with a different evidence set. Nothing happens automatically. The step people miss is the filing itself, on the assumption that being obviously Canadian is enough; the position exists only once it is filed.
Would selling my Canadian home change my snowbird position?
It can change it considerably, because the simpler route out of US residence rests on your tax home remaining in Canada. A permanent home here, with the family, the licence and the day-to-day life attached to it, is the backbone of that argument. Give it up and keep a US house instead, and the facts start to point the other way, which pushes the file towards the treaty tie-breaker rather than the closer-connection statement. If a sale is being considered, work the residency consequence out before the listing rather than at the following spring's filing.
Should my spouse and I be counted together or separately?
Separately. The test is applied to each person's own presence, so two people who travel together but not identically can reach different conclusions in the same year, and a household position covering both does not exist. Run each count across the whole look-back period. Where the answers differ, one spouse may have a filing to make and the other may not, and the Canadian returns then have to be written so the two positions sit together sensibly. Keep the day records per person as well; a single family travel diary is the usual reason this gets missed.
I work remotely from another country for a company back home — who taxes me?
Usually the country you are physically in, because employment income is generally sourced where the work is done, with your residence country taxing it as well if you are resident there and giving credit. Three things follow: your employer may acquire withholding and social security obligations where you sit, a treaty tie-breaker may be needed if both countries call you resident, and a short trip that becomes a long stay can cross a residence threshold nobody was watching. See remote workers and digital nomads.
Does my foreign spouse have to pay US tax?
Not unless something connects them to the US system: they are a citizen or green card holder, they meet the substantial presence test, they have US-source income, or you elect to treat them as a US resident so you can file jointly. That election is the one people make without weighing it, because it reaches their foreign salary, their foreign investments and their foreign accounts, not just their name on the form. See a US person with a non-resident spouse.