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 not yet in operation with no start date announced, 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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