The short answer
It depends on the jurisdiction — there is no single "183-day rule." Canada counts days in a calendar year, the UK uses its tax year (6 April–5 April), New York uses your taxable year, the US substantial presence test blends three calendar years with a weighted formula, and Schengen ignores years entirely in favour of a rolling 180-day window. Always confirm the reference period with the specific tax or border authority that applies to you.
The phrase "183-day rule" is shorthand for several different tests, and each defines its measuring period in its own way. Calendar year: Canada deems you a resident ("sojourner") if you are present 183 days or more in a calendar year, unless a tax treaty says otherwise. The US substantial presence test is also anchored to the current calendar year, but it adds a twist — it sums all your days this year, one-third of last year's days, and one-sixth of the year before, so a single calendar year is not the whole picture.
Tax year (not the calendar year): The UK Statutory Residence Test runs on the UK tax year, 6 April to 5 April; 183 days present makes you automatically UK resident, and fewer days can still mean residence through the sufficient-ties test (the "90-day tie" being one such tie, not a visa limit). Several US states use their own taxable year: New York, New Jersey, Connecticut, Massachusetts and Pennsylvania can treat you as a statutory resident if you spend more than 183 days in the state during the taxable year while keeping a permanent place of abode there. New York City applies its own version.
Rolling windows, not years at all: The Schengen short-stay rule lets non-residents stay at most 90 days in any rolling 180-day period across the whole Schengen Area, with both arrival and exit days counting as full days — a new calendar year does not reset it. Note that California has no bright-line day count at all: spending more than about nine months there creates a rebuttable presumption of residency, and the test is facts-and-circumstances.
The practical takeaways: confirm which period applies before you count, remember that day-counting rules differ (some count any part of a day, some count midnights), and know that 183 days is rarely the only test — domicile, residential ties, and centre-of-interests can make you resident on far fewer days. Border changes are also underway: the EU's Entry/Exit System has been fully operational across the Schengen Area since 10 April 2026 and ETIAS is expected later (the last quarter of 2026), but neither changes the 90/180 limit itself. This is general information, not legal or tax advice — verify your situation with the relevant authority or a qualified adviser.
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