TL;DR — Key Takeaways
- →A second passport does not cancel tax residence where you spend the year.
- →US citizenship is a worldwide filing duty regardless of where you live.
- →Treaty tie-breakers exist when two countries both claim you. They are not automatic.
- →An alert can flag the conflict. It cannot pick the winner.
Short answer
Two citizenships can mean two sets of rules at once: a filing duty from a passport, and a residency test from the country where you are physically present. Neither one turns the other off.
What usually conflicts
- A citizenship that taxes worldwide (the US is the common case) while you are also counting days toward residence somewhere else.
- Two countries whose day tests you could both meet in one year.
- A visa from one country and a tax-residency day count in another.
Tie-breaker articles in a tax treaty are for when both countries claim you. They depend on facts (permanent home, centre of vital interests, habitual abode, nationality) and on the treaty text. Domicyle alerts can warn when logged travel lines up with more than one residency clock. They do not apply a treaty.
Educational planning only — not tax advice.