Tax residency vs citizenship vs domicile: what each decides

This is the vocabulary post. If you want the whole picture first, start with Where you live, where your company is, where your money sits. Four different words all sound like “where you live” — citizenship, immigration status, tax residency, domicile — and they mean four different things. Naming them properly is most of the work, because the consequences of each are different: one is your passport, one is your permission to be somewhere, one decides which countries can tax you, and one is a long-run idea of where you belong. The single thing to hold onto: tax residency is a status you acquire by meeting a country’s rules — not one you choose, register for, or opt out of.

The four words people merge

Everyday conversation merges the four into one. They are separate legal concepts, decided by different rules, and for anyone cross-border they usually do not all point to the same country ¹.

You can be tax resident somewhere you have no right to live, and have the right to live somewhere you are not tax resident — the two are decided by different rules ¹². And tax residency is not something you file for. It is a status you acquire by meeting a country’s rules — or stop meeting them. You don’t choose it, register for it, or opt out of it; it is a consequence of facts ¹.

What tax residency actually determines

Tax residency decides which countries treat you as one of their own for tax purposes. Under residence-based taxation, a jurisdiction may tax or require residents to declare income from domestic and foreign sources. For example, UK residents normally pay UK tax on income from the UK and abroad, while Australian tax residents must declare foreign income ³⁴. That is residence taxation: a country taxes your worldwide income because you’re resident there.

The other mechanism is source taxation: a jurisdiction may tax income that, under its domestic rules, is treated as arising in that jurisdiction — including the income of a non-resident. The jurisdiction in which the income is treated as arising is commonly described as the source country ⁵³.

Countries use different combinations of the two mechanisms on different income ⁶¹. That is why the same income can be taxed twice. double taxation is a normal, expected outcome of the two mechanisms, not an error. One country taxes you because you’re resident there; another taxes the income because it arose there — both behaving correctly under their own laws ⁷. An applicable treaty, if one exists, allocates the taxing right to resolve the overlap ⁸.

Illustrative example, not a real person. Anna, a Finnish designer, is paid by a client in Germany in 2026.

In that example, the country that treats Anna as tax resident may tax or require her to declare the fee under its rules for residents’ foreign income ³⁴. A country whose domestic rules treat the fee as income arising there may also tax it on a source basis ⁵. Both claims rest on their own laws. Article 4 can determine residence for treaty purposes; the treaty article governing the particular income then determines how taxing rights are allocated ⁸.

What a tax treaty is — and isn’t

A tax treaty is a bilateral agreement between two countries that allocates taxing rights and provides a mechanism for resolving cases where both countries claim the same person as resident ⁹.

It is an allocation. It is not a way to pay no tax: a treaty assigns the taxing right between two countries, it does not remove it. A treaty generally cannot create a tax that domestic law does not impose — it limits and allocates ⁹.

It is not something you can choose to invoke. A treaty applies only where an in-force treaty covers the countries, the person, and the tax concerned ⁷. And it is not a global system: treaties are country-pair by country-pair, and not every pair has an in-force treaty ¹⁰.

When two countries both say you’re resident, the treaty runs an ordered test to decide which one wins. That ladder — the tie-breaker rules — is worth its own post The 183-day rule is not the rule. One structural point: an applicable treaty assigns residence “for treaty purposes” ⁸. It does not necessarily erase the domestic classification or every domestic filing obligation.

The tax year problem

A tax year is the accounting period a tax system uses. Countries do not all use the same tax period. The UK individual tax year runs from 6 April to 5 April, while Australia’s income year runs from 1 July to 30 June ¹¹¹². Spain and Estonia use calendar-year frameworks under the national sources already listed in this article.

So “the year you moved” is often two overlapping periods with two sets of rules.

Some systems provide split-year treatment — a mechanism that divides the moving year into a part under the old rules and a part under the new ones. The UK is one example: under its Statutory Residence Test, the year is divided only where a defined statutory case applies, and where all conditions are met, the treatment applies — it is not optional ¹³.

Other systems do not split the domestic tax year. The Spanish Tax Agency states that a natural person is resident or non-resident for the entire calendar year, because a change of residence does not interrupt the tax period ².

This is the mechanism behind most mid-year-move confusion: two tax periods overlapping in one calendar year, each running its own rules ¹³².

Exit taxation, briefly

Some countries have a rule that taxes value increases that accrued during your residence when you leave — an exit tax. It is not universal, and it is not the same thing as a final tax return ¹⁴.

As one country-specific example: Norway’s exit-tax rules may charge value increases that accrued while a person was resident in Norway for tax purposes, when the person moves abroad or to Svalbard, or transfers assets to someone living abroad ¹⁴. The applicable rules depend on when the move or transfer occurred, because the rules have changed over time ¹⁴.

This is a pointer, not a treatment. The rules are genuinely complex and differ from country to country; the point is that they exist, and that the specific rules that apply can depend on when the move happened.

What to do with this

The vocabulary now lets you do three concrete things:

1. Read your own country’s residency page and understand what it is asking — days present, a home, ties — rather than guessing ¹⁶.
2. Check whether a treaty exists for your country pair — not every pair has an in-force treaty, and the wording can differ from the OECD Model ¹⁰. That is what the Treaty Lookup tool is for. Tax Treaty Lookup — free, no signup, nothing stored.
3. Count days accurately, since days feed several of the tests — Estonia’s presence test, for example, uses at least 183 days in 12 consecutive calendar months ⁶. Tax Residency Days Tracker — free, no signup, nothing stored.

The often-quoted 183-day threshold is one test among several — not a universal rule ¹⁶. The day-counting mechanics get their own post The 183-day rule is not the rule.

This site is a set of free, browser-based tools and plain-English explanations for people who earn in one country and live in another. It is not advice, and the person behind it holds no professional credentials. Every fact is sourced and dated, and open to check. Where a question affects money, take it to a qualified accountant.

Next: the day-counting rule, and why it is not the whole story — The 183-day rule is not the rule.