Taking a job in another country changes more than your commute and your currency. It can change which government has the right to tax your salary, your savings interest, and even income you earn back home. The concept that decides this is tax residency — and it is not the same thing as your nationality, your visa, or where your employer is based.
Many people assume that spending fewer than 183 days in a country means they owe it nothing. That "183-day rule" is one of the most persistent myths in international tax. In reality, most countries use a bundle of tests — where you keep a home, where your family and economic life sit, and how many days you spend there — and a day count is only one piece. This guide explains how residency is actually determined, how double taxation is avoided, and what to check before you move.
Residency vs. nationality vs. domicile
These three ideas get muddled constantly, so it is worth separating them:
- Nationality (citizenship) is your legal relationship with a country. For most people it has no direct bearing on income tax. The main exception is the United States, which taxes its citizens and green-card holders on worldwide income regardless of where they live.
- Tax residency is a status defined by each country's tax law. It usually determines whether you are taxed on your worldwide income or only on income arising in that country.
- Domicile is a separate, longer-term concept used in some jurisdictions (notably the UK) that broadly reflects your permanent home. It can affect how certain foreign income and inheritances are treated, independent of residency.
You can be a citizen of one country, tax-resident in a second, and domiciled in a third at the same time.
How countries decide you are resident
Most residency tests combine several factors. The table below shows how three widely used systems approach it. Rules and thresholds change, so always confirm the current position with the official source before relying on it.
| Country | Core test | Day count that matters | Notes |
|---|---|---|---|
| United Kingdom | Statutory Residence Test (automatic overseas tests, automatic UK tests, then a "sufficient ties" test) | 183+ days in a tax year is automatically resident; fewer days may still be resident depending on ties | UK tax year runs 6 April–5 April |
| United States | Green-card test or Substantial Presence Test | 31 days in the current year and 183 weighted days over 3 years | US also taxes citizens abroad on worldwide income |
| Germany | Residence (a dwelling you keep and use) or habitual abode | No fixed 183-day threshold in domestic law; a long-term home can trigger residency much sooner | Habitual abode broadly means a non-temporary stay |
The UK Statutory Residence Test
The UK does not rely on a single day count. Its Statutory Residence Test works in order: first the automatic overseas tests (which can make you non-resident), then the automatic UK tests, then a "sufficient ties" test that weighs connections such as family, accommodation, work, and prior presence against the number of days you spend in the UK. Spending 183 or more days in a UK tax year makes you automatically resident with no further analysis needed, but you can also become resident with far fewer days if you have enough ties.
The US Substantial Presence Test
If you are not a US citizen or green-card holder, the Substantial Presence Test decides residency. You meet it if you are present in the US for at least 31 days in the current year and 183 or more "weighted" days across a three-year window, counting all days this year, one-third of last year's days, and one-sixth of the days from the year before that.
Illustrative example (not tax advice): Suppose someone spends 120 days in the US this year, 120 last year, and 120 the year before. The weighted total is 120 + (120 ÷ 3) + (120 ÷ 6) = 120 + 40 + 20 = 180 days. That is below 183, so on those figures alone they would not meet the test — even though the raw total across three years is 360 days.
Germany and the "dwelling" trap
Germany illustrates why the 183-day rule is unreliable as a universal test. Under German domestic law, you can become tax-resident simply by keeping a home ("Wohnsitz") that you use, or by having a "habitual abode" — a stay that is not merely temporary. Signing a long-term lease can be enough to create a filing obligation well before you hit any day count.
The 183-day rule: what it really means
The 183-day figure is real, but it is usually a tax-treaty concept, not a domestic residency test. In a typical double-taxation treaty, employment income earned by a resident of one country while working short-term in another can remain taxable only at home if three conditions all hold: the worker spends no more than 183 days in the other country in the relevant period, the pay comes from an employer that is not resident there, and the cost is not borne by a permanent establishment in that country. Miss any condition and the exemption falls away. So the rule protects certain short assignments — it does not set a blanket "under 183 days = tax-free" threshold.
Avoiding double taxation
If two countries both claim you, you are not necessarily taxed twice. Several mechanisms exist:
- Tax treaties and tie-breaker rules. Where a treaty applies and you are resident in both countries under domestic law, the treaty's tie-breaker tests (based on the OECD Model) assign residency to one country by working through a sequence: permanent home available to you, then centre of vital interests (personal and economic ties), then habitual abode, then nationality, and finally mutual agreement between the tax authorities.
- Foreign tax credits. Many countries let you credit tax already paid abroad against domestic tax on the same income, so you effectively pay the higher of the two rates rather than both in full.
- Exemptions and exclusions. Some systems exempt qualifying foreign income. US citizens abroad, for example, may use the Foreign Earned Income Exclusion (Form 2555) to exclude up to $130,000 of foreign earned income for the 2025 tax year if they meet the bona fide residence test or the physical presence test (330 full days abroad in a 12-month period). Passive income such as dividends, interest, and pensions does not qualify.
Which mechanism applies depends on the specific treaty and the two countries involved, so the same move can be handled very differently depending on the pairing.
A practical checklist before you move
- Identify both countries' domestic residency rules — day counts, home/dwelling tests, and any ties tests.
- Check whether a tax treaty exists between them and read its tie-breaker and employment-income articles.
- Track your days precisely, including partial days, since thresholds can turn on a single day.
- Keep evidence of where your home, family, and economic life sit — leases, utility bills, employment contracts.
- Model your take-home pay in each scenario. Our salary calculator and our comparison of take-home pay in the US, UK, and Germany can help you estimate the gross-to-net difference before you commit.
To go deeper on the underlying mechanics, see our explainer on how income tax works and our guide to social security contributions, which are handled separately from income tax and often follow their own cross-border rules.
Final thoughts
Tax residency is decided by a combination of tests — home, ties, economic life, and days — and the 183-day rule is only a fragment of that picture, often relevant mainly inside tax treaties. Double taxation is usually avoidable through treaties, foreign tax credits, and exclusions, but the outcome depends heavily on the specific countries and the treaty between them.
The figures and thresholds in this guide reflect the tax years indicated and can change from year to year; rates, allowances, and even the tests themselves are periodically revised. Nothing here is personalised tax advice. Before you act on a move abroad, confirm the current rules with the official tax authorities in both countries and consult a qualified cross-border tax professional about your own situation.