How the calculation works
Tax residency determines where you owe tax on your worldwide income, and it is decided by physical presence far more than by your visa type or nationality. This tool applies the two tests that matter most to globally mobile people. The first is the international 183-day rule used by the majority of countries; the second is the United States' more elaborate Substantial Presence Test. Because the US counts part of your days from previous years, you can become a US tax resident even in a year when you spent fewer than 183 days there, which surprises many people.
The 183-day rule
Most countries treat you as resident if you are present for 183 days or more in their tax year. It sounds simple, but the details differ: some countries count any day on which you are present at midnight, others count any part-day, and the tax year may not align with the calendar year. Several countries also add secondary tests based on where your home, family or economic interests are. This tool uses the 183-day threshold as a clear baseline, but you should check the precise definition in each country you spend significant time in.
The US Substantial Presence Test
The US formula weights three years. It counts every qualifying day this year, one-third of last year's days and one-sixth of the days from two years ago. If that weighted total is 183 or more and you were present at least 31 days this year, you generally meet the test. The weighting means consistent visits of around four months a year can tip you into US residency over time. The calculator shows your weighted total so you can see how close you are and plan future trips accordingly.
How to manage your residency position
If the result puts you near or over a threshold, there are legitimate ways to plan. Track your days precisely with a calendar or app, because tax authorities expect evidence such as boarding passes and entry stamps. Learn whether your country counts arrival and departure days. If you genuinely live elsewhere, the US closer-connection exception or a tax-treaty tie-breaker may keep you non-resident, but both require filing the right forms on time. Beware of dual residency, where two countries each claim you - a tax treaty usually decides the winner, but only if you invoke it correctly.
This estimate is a starting point, not a ruling. Exempt-individual rules, treaty provisions and country-specific tests can all change the outcome, and getting residency wrong can lead to double taxation or penalties. Use the figures here to understand your exposure, then confirm your status with a qualified cross-border tax adviser before making decisions.