Tax residency determines which country has the right to tax your worldwide income. Most countries use the 183-day rule — spending 183 or more days in a country during a tax year generally makes you a tax resident there. However, the rules vary significantly: France considers your principal home and economic interests, the UK uses the Statutory Residence Test (SRT) with automatic and sufficient ties tests, and the US taxes citizens regardless of residency through the Substantial Presence Test.
What does the 183-day rule really mean for tax residency?
The 183-day rule is one of the most misunderstood concepts in international taxation. Many people believe that staying under 183 days in a country automatically means they're not tax resident there. This is often wrong. In France, meeting just one of four alternative criteria (family home, principal stay, professional activity, or economic interests) is sufficient, regardless of the number of days. In the UK, the Statutory Residence Test combines day counting with a "sufficient ties" analysis. In the US, days are weighted across three years.
What are the four criteria for French tax residency?
France uses four alternative criteria — meeting any one establishes residency. The foyer criterion (family home) is the strongest: if your spouse and children live in France, you're likely tax resident even if you work abroad most of the year. The séjour principal criterion considers relative presence: spending more days in France than in any other single country can trigger residency, even below 183 days.
How does the US Substantial Presence Test work?
The US counts days using a weighted formula over three years: current year × 1 + prior year × 1/3 + two years prior × 1/6. If the total reaches 183 and you spent at least 31 days in the current year, you meet the Substantial Presence Test. A "closer connection" exception may apply if you can demonstrate stronger ties to another country.
How do tax treaties prevent double taxation?
When dual residency applies, bilateral tax treaties provide tie-breaker rules following a hierarchy: permanent home → center of vital interests → habitual abode → nationality. The treaty determines which country has primary taxing rights for each income type.
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