The 183-day rule & tax residency, explained
How tax residency really works — the 183-day rule, each country's fiscal year, the US substantial presence test, the UK ties test, and the days-counting that decides what you owe.
Where you are tax resident usually decides what you owe — and for most people, residency comes down to one thing: how many days you spent in a country. The headline is the 183-day rule: spend 183 days or more in a country in its tax year and you are generally tax resident there.
But "generally" hides a lot, and that's where people get caught:
- The tax year differs by country — the UK runs 6 April to 5 April, Australia 1 July to 30 June, most others the calendar year. Your day count has to line up with the right window.
- Some countries look beyond days at your home, family and work ("centre of vital interests") and can make you resident regardless of the count.
- The UK lowers the 183 threshold based on how many "ties" you have. The US taxes citizens worldwide and uses a weighted substantial presence test.
- You can be resident in more than one country at once — and double-counting days is exactly how an accidental second residency happens.
This pillar covers the rules travellers ask about most:
- What is the 183-day rule, and how does it work?
- The US substantial presence test
- The UK Statutory Residence Test and ties
Where Flags fits
Flags: Tax Residency counts your days in every country and all 51 US states from the dates in your photos — on your iPhone, offline, no GPS — and compares each against its own threshold and fiscal year. It flags home/family/work ties as a Review, handles the UK ties grid, and warns when you drift toward a line in a country you weren't even watching.
Flags is an early-warning tool, not tax advice. It deliberately simplifies: it does not model tax treaties, the US weighted substantial-presence formula, the Foreign Earned Income Exclusion, or every special regime. Always confirm your position with a qualified adviser. See the flag-strategy guide for the bigger picture.
In this guide
- What is the 183-day rule, and how does it actually work?The 183-day rule makes you tax resident once you spend 183 days in a country's tax year — but the tax year, what counts as a day, and "ties" all change the answer. Here's how it works.
- The US substantial presence test, explainedThe US doesn't use a flat 183 days — it weights the last three years. Here's how the substantial presence test works, the closer-connection exception, and how to track the days it relies on.
- The UK Statutory Residence Test and ties, explainedThe UK doesn't use a flat 183 days — your "ties" can drop the threshold to 45. How the Statutory Residence Test works, the sufficient-ties table, and tracking the days it depends on.
- How to track your tax-residency days (the easy way)Spreadsheets fail at day-counting for tax residency because you stop updating them. How to track days per country reliably — automatically from your photos, with each country's threshold and fiscal year.