Glossary
The vocabulary of day counting, in plain language — the terms border officers, tax authorities, and calculators all assume you already know.
Residency concepts
- Tax residency
The status that makes a country or state entitled to tax you as a resident — usually on worldwide income. Every jurisdiction sets its own test, and you can be a tax resident of more than one place at the same time.
- Domicile
Your permanent legal home — the place you intend to return to indefinitely. Unlike residency, you have exactly one domicile at a time, and in many jurisdictions (New York, the UK) it matters as much as your day count.
- Statutory residency
Residency created by a mechanical rule rather than by where your life is centered — typically a day count plus a dwelling, such as New York's 183-days-plus-permanent-place-of-abode test.
- Deemed residency
Residency assigned to you by a rule even when you don't meet the ordinary test — for example, Canada deems certain long-stay sojourners to be residents for the year.
- Dual residency
Being a tax resident of two jurisdictions at once under each one's domestic rules. It happens often and is usually resolved by a tax treaty tie-breaker — or by paying attention to both sets of rules.
- Part-year resident
Someone who was a resident of a state or province for only part of the tax year because they moved in or out. Most US states tax part-year residents only on income earned during the resident portion.
- Statutory domicile
The formal, legal version of domicile as defined by a specific statute — the concept a tax authority applies when it decides where your permanent home is, regardless of where you spent the most nights.
- Center of vital interests
A treaty concept for the place where your personal and economic ties are strongest — family, work, property, community. It is the first tie-breaker most tax treaties use when two countries both claim you.
- Habitual abode
The place where you live regularly in the ordinary course of life — the second tie-breaker in most tax treaties, applied when your center of vital interests is unclear.
- Non-dom
Short for non-domiciled — a UK status for residents whose permanent home is abroad. Non-doms historically could limit UK tax on foreign income; the regime was replaced from April 2025 by a residence-based system.
Day-count rules
- 183-day rule
The bright-line threshold used by many countries and states: spend 183 days (roughly half the year) or more in a place during a year and you become its tax resident. Simple to state, easy to miscount.
- Substantial presence test
The IRS formula for US tax residency: at least 31 days in the US this year, plus a weighted total of 183 days across the current and two prior years (current year counts full, prior year one-third, year before one-sixth).
- Schengen 90/180 rule
Short-stay visitors may spend at most 90 days inside the Schengen area in any rolling 180-day window — counted across all Schengen countries combined, not per country.
- Rolling window
A counting period that moves with you: instead of a fixed calendar year, you look back N days from today. Schengen's 180-day window is rolling, which is why a spreadsheet with year totals gets it wrong.
- Midnight rule
The convention that you are counted in the place where you were at midnight. Most day-count regimes use some version of it, which makes arrival and departure days count differently than people expect.
- Partial days
Days on which you cross a border. Some rules count any part of a day as a full day of presence; others ignore transits. The difference can swing a residency test by weeks.
Visas & borders
- Visa-free
Permission to enter a country for short stays without any visa at all, usually capped at a fixed number of days (30, 90, 180). Visa-free is an entry permission, not a right to work or reside.
- Visa waiver / ESTA
A pre-travel electronic authorization for visa-free travelers — the US calls it ESTA, the EU's version is ETIAS. It is not a visa, but travel without it is refused at check-in.
- Residence permit
An immigration document allowing you to live in a country beyond the short-stay visa-free limit. Holding one usually changes both your border rights and your tax position.
- Golden visa
A residence permit granted in exchange for a qualifying investment — property, funds, or business. Several EU states have tightened or ended their programs since 2023; rules change fast.
- Green card test
The other US tax-residency test besides substantial presence: if you hold lawful permanent resident status at any point in the year, the US treats you as a tax resident regardless of days present.
US tax
- Abode
In US tax law, your home in the everyday sense — where you maintain your domestic life. The IRS definition of tax home and abode decides whether expatriates qualify for the foreign earned income exclusion.
- FEIE (Foreign Earned Income Exclusion)
The US provision letting qualifying citizens and residents abroad exclude a capped amount of foreign-earned income from US tax. Qualifying requires passing either the bona fide residence test or the physical presence test.
- Tax home
Your principal place of business or employment — the IRS concept that determines whether you are "away from home" and, for expatriates, whether the FEIE applies.
- Physical presence test
One way to qualify for the FEIE: be physically present in a foreign country or countries for at least 330 full days during any 12 consecutive months. Full days means midnight to midnight abroad.
- Bona fide residence test
The other FEIE qualification: being a bona fide resident of a foreign country for an uninterrupted period covering an entire tax year. It is a facts-and-circumstances test, not a day count.
- Exit tax
A tax triggered by giving up a status — most famously the US expatriation tax on citizens and long-term green card holders who renounce, which treats assets as sold at fair market value.
- Tax treaty
A bilateral agreement that overrides domestic law to prevent double taxation — defining which country may tax what, and how to break the tie when both claim you as a resident.
- Tie-breaker rule
The ordered tests inside a tax treaty that assign dual residents to one country: permanent home, then center of vital interests, then habitual abode, then nationality.
- Permanent establishment
The treaty concept that decides when a business becomes taxable in another country — a fixed place of business or a dependent agent. Working remotely from abroad can raise this question for your employer.
International terms
- Jour de présence
French for "day of presence" — the unit France and francophone countries count for their residency tests. The concept is the same everywhere; only the language and the threshold change.
- Wohnsitz
German for "residence" — a dwelling you keep and actually use, which under German law can establish tax residency alongside the 183-day style tests. Austria and Switzerland use the same concept.
These definitions are orientation, not tax or legal advice — the linked pages carry the detail and the official sources. For exactly how days are counted, see the counting methodology.
The app that speaks this language fluently
Day31 for iPhone applies these rules to your actual travel history automatically — every term on this page becomes a number you can watch, with a warning before it becomes a problem.