183-Day Rule

The 183-day rule is the main quantitative test for establishing Portuguese tax residency. If an individual spends 183 or more days in Portugal during any 12-month period beginning or ending in a given tax year, they are deemed a Portuguese tax resident for that year and subject to IRS on their worldwide income. The day count includes any partial days — arrival and departure days each count as one. There is also a secondary test: having a habitual residence (habitação habitual) in Portugal on 31 December of the year, even with fewer than 183 days present. Tax treaties with other countries may override or modify this domestic rule, particularly the 'tie-breaker' clauses in double taxation agreements.