Tax residency is the status that determines which country has the primary right to tax a person's income, and often their worldwide income rather than only locally sourced income. Countries set their own tests, but they commonly look at how many days you spend there, whether you maintain a permanent home, and where your centre of vital interests — family, work and economic ties — lies.
Worked example
Suppose a country treats you as resident if you are present for 183 days or more in a calendar year. You spend 120 days in Country A and 200 days in Country B. Under a simple day-count test you are resident in Country B (200 ≥ 183) and non-resident in Country A (120 < 183), so Country B has the primary right to tax your worldwide income.
Why it matters
Tax residency matters because it usually decides whether a country taxes only your local income or your entire worldwide income, which can mean a large difference in your total bill. The pitfall is assuming citizenship or a visa equals tax residency: they are separate concepts, and it is possible to be treated as resident by two countries at once, which is why tax treaties include tie-breaker rules.
Frequently asked questions
No. Citizenship is a legal nationality, while tax residency is determined by factors such as days of presence and where your home and life are based. You can be a citizen of one country and a tax resident of another.
Yes, if each country's domestic test treats you as resident. In that case, a tax treaty between the two countries typically applies tie-breaker rules — such as permanent home and centre of vital interests — to assign a single residency. This is general information, not personal tax advice.