DoubleTaxationMethodology: how we determine tax residence
This page explains how the service reaches its conclusion, where the rules come from and how we check them.
Who reviews the rules
PhD Yevhen Marynchak — tax residence lawyer; responsible for the service's rules, sources and texts.
How the check works
For each country the rules are written as a sequence of questions under its law: home, centre of vital interests, days of presence, citizenship, registration and so on. You answer the questions, and the engine walks through the rules of both countries and shows what each law says.
If both countries treat you as their resident, the double tax treaty applies (Article 4): permanent home → centre of vital interests → habitual abode → nationality → mutual agreement between the tax authorities. If there is no treaty, or it has no such rule, the service says so.
The conclusion is produced by the rules engine, not by an AI model. Your answers are processed in your browser and are not sent to a server.
Sources
Primary sources only: current texts of laws, treaty and protocol texts, tax authority guidance and decisions of the highest courts (2019–2026). Reviews by consulting firms are used only to find sources, never as the legal basis.
Every conclusion lists the provisions it relies on, with links to the official texts.
How we check the data
Each set of rules and guidance is checked separately: a second, independent review compares every figure, deadline and provision with the primary source. Discrepancies are corrected or flagged for the lawyer's decision; disputed points are not published as fact.
Automated tests (more than 1,500) check the rules of all 12 language versions before every release: every country against every other, day thresholds, the order of treaty criteria and tax calculations.
Reliability of the conclusion
The scale shows how clearly your circumstances fit the statutory and treaty criteria; it is not a statistical probability.
The starting value depends on the confidence level of the rule: "determined" — 95%, "probable" — 80%, "disputed" — 55%. If the two countries' laws disagree and the treaty decides — minus 5. Each "I don't know" answer — minus 5 (no more than 15 in total). The score is never below 30% or above 97%.
Special cases: resident of both countries — 60%, mutual agreement between tax authorities needed — 50%, status not determined — 35%. If court practice affects the conclusion, this is stated next to the scale.
Tax burden and business forms
The tax burden on salaries follows the OECD Taxing Wages method: income tax including local taxes plus employee contributions; a single person without children; ECB exchange rate of 2 January. Business forms are compared for one activity (IT and consulting for companies) with the same assumptions, listed on each page.
Updates and corrections
Rules are updated when a law, treaty or case law changes; tax parameters every January and OECD indicators every May. Pages show the date of the last check.
If you spot a mistake or an outdated provision, tell us through the feedback form; we will check and correct it.