US Substantial Presence Test calculator
The Substantial Presence Test decides whether you are treated as a US resident for tax purposes. It is not a simple 183 days in one year — it is a weighted formula across three calendar years, which is why people are caught by it without ever spending half a year in the country.
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How the rule actually works
The formula weights three years.
All of your days this year, plus one third of last year's days, plus one sixth of the days from the year before that.
Two conditions must both be met.
At least 31 days in the current year, and a weighted total of 183 or more across the three years.
It runs on calendar years.
Unlike the UK, there is no April boundary — 1 January to 31 December.
Some days do not count at all.
Days as an exempt individual (certain visa categories), days you could not leave because of a medical condition that arose in the US, and regular commuting days from Canada or Mexico are excluded. This calculator counts every day entered.
Frequently asked
How is the Substantial Presence Test calculated?
Count all days of US presence in the current year, add one third of the days in the prior year and one sixth of the days in the year before that. If the total reaches 183 and you had at least 31 days in the current year, the test is met.
Does a partial day in the US count?
Yes. Any part of a day physically present in the United States counts as a full day, with limited exceptions.
Does meeting the test mean I owe US tax?
It means you are treated as a US tax resident for the year, which brings worldwide income into scope. The closer-connection exception and tax treaties may change the outcome — this is the point to take professional advice.
What is the closer connection exception?
If you were present fewer than 183 days in the current year and can show a tax home and closer connection to another country, you may be able to avoid resident status by filing Form 8840.