Tax residence is decided by counting, and every country counts differently
Nguyễn Đình Tuệ
A new residence card, a second passport or a long lease does not move a tax obligation. Three major authorities use three different tests, and a person can cross the line in two of them in the same year.
For an investor with more than one place to live, the hard question is not where to be but where tax residence falls. A new residence card, a second passport or a long lease does not move a tax obligation by itself. The revenue authority looks at a set of facts — days present, where a permanent home is kept, where family and income are anchored — and only then reaches a conclusion. Getting that order wrong is the root of most of the trouble that follows.
Three ways of counting, read from the revenue authorities
| Jurisdiction | Day threshold | Other criteria that decide the case |
|---|---|---|
| United States | 31 days in the current year, and 183 days on a weighted formula | The formula: All days this year, plus one third of the days in the preceding year, plus one sixth of the days in the year before that |
| United Kingdom (becoming resident) | 183 days or more in the tax year | A sole UK home for 91 consecutive days with at least 30 days spent in it; or full-time UK work across 365 consecutive days |
| United Kingdom (leaving residence) | Fewer than 16 days; or fewer than 46 days if not UK resident in the previous three tax years | Full-time work abroad with fewer than 91 days in the UK, of which no more than 30 were working days |
| Vietnam | 183 days in a calendar year, or within 12 consecutive months from the date of arrival | A habitual residence: Registered permanent residence, a temporary residence card, or leased accommodation for 183 days or more in a year |
Read from the IRS, GOV.UK and Circular 111/2013/TT-BTC on 19 August 2026. Three jurisdictions, three different methods of counting — which is why a person can cross the threshold in two places in the same year.
Tax residence and immigration status are not the same thing
The two share a word and belong to different bodies of law. Immigration status answers how long a person may stay and what they may do. Tax residence answers which state may tax their worldwide income. A person can hold permanent residence in one country and be tax-resident in another, and the authority that issues the card is usually not the authority that decides the tax question.
What the tests actually measure
Each authority is looking for the same thing by different means: Whether the centre of a life sits inside its territory. Day counts are the most visible instrument but rarely the only one. A home, a family, a source of income and a place of habitual abode all carry weight, and in some systems they decide the case where the day count alone does not.
The tests cluster around four groups of facts, which are not mutually exclusive; many systems apply several at once, in their own order of priority. Days of physical presence, measured against the threshold set in domestic law. A permanent home, meaning somewhere kept available for lasting use, owned or rented. The centre of vital interests, meaning where the family, the main economic activity, the accounts, the businesses and the durable social ties sit. And nationality or place of registration, which some systems use as an additional or substituting layer.
The day threshold, the treatment of part days, the handling of a transition year and the definition of a permanent home are all numbers and wording of domestic law. They move with each amendment, which is why they are worth reading at the authority rather than in a third-party summary.
When two countries both claim you
Because the tests differ, overlap is normal rather than exceptional. Someone spending a third of the year in each of three places can satisfy more than one definition at once. That is what double-taxation treaties and their tie-breaker rules exist to resolve, and it is also why the resolution depends on facts a person should be recording as they go rather than reconstructing afterwards.
The reference framework behind most bilateral treaties is the Model Tax Convention on Income and on Capital published by the OECD. Its tie-breaker sequence runs from the permanent home, to the centre of vital interests, to the habitual abode, to nationality, and finally to agreement between the two tax authorities. Two things are worth holding on to: a treaty only applies where one exists between the exact pair of countries involved, and any given treaty can depart from the model text.
Why immigration paperwork does not settle it
Investors often assume a residence permit either creates or removes a tax obligation. It does neither by itself. It changes where a person is entitled to be, which in turn changes the facts the revenue authority will weigh — but the weighing is done under tax law, against tests the permit does not mention.
Many investor-residence programmes require only a minimal presence, and some almost none. That is enough to keep the card and not enough for a state to treat the holder as tax resident, nor enough for the previous country to stop treating them as one. In the other direction, some revenue authorities operate a preferential regime for new arrivals; the conditions, the duration and the scope differ between countries and should not be inferred from one to another. The document a bank or a counterparty asks for is the tax residence certificate issued by the revenue authority, not the residence card.
What to check
Count days across the whole calendar or tax year rather than the part that suits the answer, and keep the entry and exit evidence. Read the test in the words the authority itself publishes, for every country involved. Where two claims are possible, read the treaty tie-breakers before assuming which one wins. And check when each tax year starts, because they do not all start in January.
The largest risk is not the rate but the gap in the record. Four things are worth putting on the same measure before moving: the rules under which the current country of residence ends that status, including the duty to file for the final year; whether a charge arises on leaving in respect of unrealised gains, in the countries that have one; the automatic exchange of financial account information between revenue authorities; and the evidence of presence itself — tickets, entry and exit stamps, leases, utility bills, school records.
Tax residence is a conclusion drawn from facts, not an entitlement attached to a card. The map of days, homes and interests is worth drawing before anything is signed, then checking against the original text of each revenue authority and the relevant bilateral treaty.
The Legation Times writes its content from published documents; nothing here is legal, tax or investment advice. Spotted an error? Send a correction request; for content rights, send a takedown request.
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