The expat day counter guide: residency, treaties, and the rules you'll actually face
If you're an American living abroad, a Brit in the EU, or anyone with a foreign tax home, day counts decide where you owe tax. Here's the playbook for tracking residency thresholds and treaty tie-breakers.
Living abroad doesn't end your tax life, it complicates it. As an American expat you still file with the IRS no matter where you live. As a Brit in the EU you may face the UK's Statutory Residence Test alongside whatever your new country imposes. Treaty tie-breakers exist to prevent double taxation, but applying them requires defensible day counts.
Rules every expat should track
- Home-country residency rule, if you're trying to leave, the threshold to fall under (UK SRT, Australian residency, Canadian significant ties).
- New country's 183-day rule, most countries trigger residency at 183 days.
- Schengen 90/180, if your new home is the EU and you're a non-EU citizen.
- US Substantial Presence Test, if you're a non-US citizen visiting the US.
- Treaty residency tests, when both countries claim you, the tax treaty's tie-breaker decides.
Americans abroad: special rules
US citizens are taxed on worldwide income regardless of where they live. The Foreign Earned Income Exclusion (FEIE) lets you exclude up to ~$130K (2026) of foreign earned income, but it requires either:
- Bona Fide Residence Test: you're a bona fide resident of a foreign country for an uninterrupted tax year.
- Physical Presence Test: you're physically present in foreign countries for at least 330 full days during any 12-month period.
The Physical Presence Test is the more common path. 330 days × 24 hours = strict counting. Days you're in the US, in international airspace, or on the high seas don't count as 'foreign country' days. Manual tracking is essential.
FEIE day counting is unforgiving. Lose track and miss the 330-day threshold by even one day, and the entire exclusion is forfeited. The penalty is real money, for a $200K earner, ~$30,000 in tax.
Leaving home: the departure test
If you're a Brit, Canadian, Australian, or non-citizen US resident moving abroad, your home country has rules to determine when you actually 'left' for tax purposes. Examples:
- UK: the SRT determines residency by ties and day count. Below 16 UK days you're automatically non-resident if you were UK-resident in any of the last 3 years.
- Canada: the CRA looks for severance of significant ties, home, spouse, children. Day count alone isn't enough.
- Australia: domicile and 183-day tests interact. The ATO scrutinizes departures to low-tax jurisdictions.
Treaty tie-breakers
If you're a tax resident of two countries under their domestic rules, the relevant tax treaty's residency article picks one. The OECD model tie-breaker (used by most treaties) applies in this order:
- Permanent home, where do you have a permanent home available?
- Center of vital interests, where are your personal and economic ties stronger?
- Habitual abode, where do you usually live?
- Citizenship, last resort.
- Mutual agreement, if all else fails, the two competent authorities decide.
Each step needs evidence. Day counts feed 'permanent home' (which one is more available?), 'center of vital interests' (where is the economic activity?), and 'habitual abode' (which one do you live in more?).
The base strategy
- Pick a tax home and commit. Don't be a tax resident of nowhere, that's an audit magnet.
- Track every country you visit. Schengen, US SPT, UK SRT all count overlapping days.
- Sever home-country ties methodically. Driver's license, voter registration, primary doctor, accountant.
- Document foreign-country ties. Lease, utility bills, local bank, local tax registration.
- Get a Certificate of Tax Residence. Most countries issue one; treaty partners require it.
Common expat mistakes
- Spending too many days back home. 'Just for Christmas' becomes 30 days, and 30 days × 4 visits = enough to break the FEIE 330.
- No CRT or proof of foreign residency. When the IRS asks for evidence, you have nothing.
- Maintaining a home-country abode. NY, NJ, MA, CT all use abode + day count for statutory residence.
- Reconstructing day counts at tax time. Auditors won't accept 'I think I was abroad in March.'
- Mixing up Schengen and country-specific days. 89 Schengen days could be 89 Spain days, both rules apply.
The tracker built for expats
Tax Days tracks every threshold an expat faces: home-country departure rules, new-country 183-day rules, Schengen 90/180, US SPT (if relevant), FEIE 330-day windows, and treaty tie-breaker evidence. Add a trip and the app updates every applicable window in real time.
Build the day-count habit on the day you move. The FEIE Physical Presence Test, the UK SRT, and your new-country residency test all start counting immediately.
Frequently asked questions
Do American expats still have to file US taxes while living abroad?
Yes, generally. US citizens are taxed on worldwide income regardless of where they live, so moving abroad doesn't end your IRS filing obligations. The Foreign Earned Income Exclusion can let you exclude up to roughly $130K (2026) of foreign earned income, but only if you qualify under the Bona Fide Residence Test or the Physical Presence Test.
How does the FEIE Physical Presence Test work?
You must be physically present in foreign countries for at least 330 full days during any 12-month period, and the counting is strict. Days spent in the US, in international airspace, or on the high seas generally don't count as foreign-country days, which is why careful tracking is essential.
What happens if I miss the 330-day threshold by one day?
Missing the 330-day threshold by even a single day generally forfeits the entire exclusion, not just part of it. For someone earning $200K, that can mean roughly $30,000 in additional tax, so short trips home (like holiday visits that stack up to 30 days each) deserve careful counting.
How do treaty tie-breakers decide which country I'm a resident of?
When two countries both claim you under their domestic rules, the treaty's residency article picks one, and most treaties follow the OECD model order: permanent home, then center of vital interests, then habitual abode, then citizenship, and finally mutual agreement between the two tax authorities. Each step needs evidence, and your day counts feed the analysis at every stage.
What documents prove my foreign tax residency?
A Certificate of Tax Residence is generally the key document: most countries issue one, and treaty partners require it. Beyond that, documented foreign ties (a lease, utility bills, a local bank account, local tax registration) plus a contemporaneous day-count log give you evidence when the IRS or your home country asks for proof.