The "183-day rule" isn't one law. It's a threshold that appears in many countries' tax rules and in tax treaties: spend about 183 days or more in a country, a little over half a year, and it may treat you as tax resident or gain the right to tax your pay. What counts as a day, which 12 months are measured and what else matters all differ from country to country, so always check with the tax authority of the country concerned.
This page is general information, not tax advice. For your own situation, talk to a tax adviser who knows both countries.
Three common versions
The same number shows up in very different rules. Three that affect many travelers:
| Rule | Where the 183 days come in | How a day counts |
|---|---|---|
| UK Statutory Residence Test | 183 or more days in the UK in a tax year (6 April to 5 April) makes you automatically UK resident | A day counts if you are in the UK at the end of it (midnight), with exceptions such as transit |
| US substantial presence test | At least 31 days this year, and 183 days over three years using a weighted sum | Any part of a day counts, with exceptions |
| Tax treaties on the OECD model (Article 15) | Pay for work done in another country stays taxable only at home if you are there no more than 183 days in any 12-month period starting or ending in the tax year, among other conditions | Set by each treaty and each country's practice |
The UK: 183 midnights
In the United Kingdom, under the Statutory Residence Test, you are automatically UK resident for a tax year if you spend 183 or more days in the UK during it. HMRC counts a day as a day in the UK if you're there at midnight. Fewer days don't guarantee you're non-resident: the UK has other tests, based on your home, your work and your ties to the country, that can make you resident with far fewer days.
The US: a weighted three-year sum
For the United States, the IRS's substantial presence test asks two things. Were you in the US on at least 31 days this year? And do these add up to 183 or more:
- all the days you were present this year,
- one third of the days last year,
- one sixth of the days the year before that.
Any part of a day counts. There are exceptions, for example for regular commuters from Canada or Mexico, for transit of under 24 hours between two places outside the US, for some students, teachers and diplomats, and for days you couldn't leave because of a medical condition. A "closer connection" exception can also apply.
Tax treaties: who taxes your salary
Many tax treaties follow the OECD's model. Its Article 15 says that pay for work done in another country is taxed only in your home country if three conditions are all met: you are there for no more than 183 days in any 12-month period starting or ending in the tax year, your employer isn't resident there, and your pay isn't borne by a branch your employer has there. Each treaty has its own wording, so read the one between your two countries.
Worked example 1: the US weighted sum
A consultant spends 120 days in the US in each of 2024, 2025 and 2026.
- 2026: 120 days counted in full = 120
- 2025: 120 ÷ 3 = 40
- 2024: 120 ÷ 6 = 20
- Total: 180, under 183. The test is not met for 2026.
Change 2026 to 125 days and the total becomes 125 + 40 + 20 = 185. The test is met, unless an exception applies. Five extra days in one year tipped the result, which is why people near the line keep exact records.
Worked example 2: the same stay, two answers
Someone arrives in London on 3 October 2026 and flies out on the morning of 3 April 2027, inside the UK tax year that runs from 6 April 2026 to 5 April 2027.
- Counted by midnights, the UK way: 182 days. Under the automatic 183-day test.
- Counted by any part of a day, the US way: 183 days.
Same trip, one day apart, and that one day sits right on the line. Note too that 182 midnights doesn't settle UK residence: the UK's other tests still apply.
Myths worth dropping
- "Under 183 days anywhere means I'm not resident anywhere." No. Countries also look at where your home, family and work are. And some countries tax by citizenship: the IRS says US citizens living abroad are taxed on their worldwide income.
- "It's per calendar year." The UK uses a tax year from 6 April. Treaties on the OECD model use any 12-month period starting or ending in the tax year. The US weighs three years.
- "183 days is six months." Six calendar months can be anywhere from 181 to 184 days.
- "If I hit 183 days I stop being resident at home." Not by itself. You can be resident in two countries at once; many treaties have tie-breaker rules for that case, in the OECD model's Article 4.
Keep a count you could defend
If you're anywhere near a threshold, keep a log as you go rather than rebuilding it later:
- Note each date you enter and leave a country, and if you were there at midnight.
- Keep proof: boarding passes, booking emails, passport stamps where they still exist, card statements. Since 10 April 2026, Schengen entries are recorded electronically instead of stamped.
- Keep your iPhone saving photo locations, and Google Maps Timeline on if you use it, as a second record.
- Count both ways, any part of a day and midnights, so you know your number under either rule.
The days-in-country calculator does the counting from your dates, and how to count the days you've spent in each country shows how to build the log. A flight log helps too. Globestamp keeps days in every country, with a 183-day alert (a Pro feature), which is a handy early warning but not a substitute for the records a tax authority may ask to see.
Where to check the real rules
- UK: HMRC's guidance on the Statutory Residence Test, on GOV.UK.
- US: the IRS page on the substantial presence test, and on taxes for citizens abroad.
- Anywhere else: the national tax authority's own site, and the text of the tax treaty between the two countries.
If you're also counting days for travel rules rather than tax, that's a different count: see the Schengen 90/180-day rule.