How the IRS counts days
You meet the substantial presence test if you were physically in the US at least 31 days this year and at least 183 days over three years, counting all days this year, one third of last year's days and one sixth of the days the year before. Any part of a day in the US counts as a day.
A snowbird who spends 150 days a year in Florida reaches 150 + 50 + 25 = 225 weighted days and meets the test, even though each year is under six months. About 121 days a year every year stays under 183.
Days that do not count
- Days you regularly commute to work in the US from a home in Canada or Mexico.
- Days in transit through the US for less than 24 hours.
- Days you could not leave because of a medical condition that started in the US.
Closer connection exception, Form 8840
If you meet the test but spent fewer than 183 days in the US this year, you can still be treated as a nonresident if you keep a tax home in another country and have a closer connection to it. You must file Form 8840 by the due date of Form 1040-NR. If you do not file it on time, you lose the exception.
Canada–US treaty tie-breaker
A Canadian who spends 183 days or more in one year cannot use Form 8840. The Canada–US tax treaty has tie-breaker rules for people both countries treat as residents, based on where you have a permanent home and closer personal and economic ties. Claiming it is done on a US nonresident return with Form 8833.
Provincial health coverage
Each province sets its own limit on time outside Canada before you can lose health coverage, so check your province before planning a longer winter. This page is an estimate; confirm with a cross-border tax professional.
Questions
I stay under six months a year. Am I safe?
Not necessarily. Around 150 days every year adds up to more than 183 weighted days. Below about 121 days a year in each of three years you stay under the test.
Does meeting the test mean I owe US tax on everything?
Not if you qualify for the closer connection exception with Form 8840, or claim treaty residence in Canada. Without one of those, US residents are taxed on worldwide income.
Is this the same as the 183-day rule for my province?
No. Provincial health plans have their own rules on time out of the country, and they vary by province.
