Research methodology
Where our numbers come from, how we verify them, how we estimate costs, and what our method cannot tell you.
Where our numbers come from, how we treat them, and what they cannot tell you.
Primary sources, named
For anything with legal or financial consequences we use the body that sets the rule, not a summary of it. For Spain that means the ministries, the tax agency, the social security administration, the central bank and the official gazette. For American tax obligations that continue abroad, it means the IRS.
We name the responsible body next to every link. Linking a ministry page without saying who publishes it is half a citation.
The source register
Every source is a record, not a link. Each record holds the official URL, the responsible body, the jurisdiction, the date we consulted it, the date a human last verified it, the single claim it supports, its editorial status and the name of its reviewer.
One claim per record. This is deliberate and it is the most useful thing we do. When a government page changes, we can see immediately which claims across which guides now need re-checking, rather than rereading everything.
A source that has not been verified by a person is never shown to you, and never satisfies the check that lets a page carrying sensitive claims go live.
How we estimate costs
Cost figures are the softest data on this site and we label them as such everywhere they appear.
- We present ranges where a range is honest, and we resist the pressure to give a single reassuring number.
- Our calculator states publicly the date its default values were last reviewed. An undated assumption is worth nothing to you.
- We do not model tax, income or currency movement, and we say so on the tool itself. Exchange rates alone can move a dollar-denominated budget by ten per cent inside a year.
- Rent is treated as a household cost; insurance and daily living as per-person. These assumptions are written out in full on the calculator rather than buried in code.
How we compare cities
We compare on factors we can observe and describe: size, climate, language environment, transport, housing pressure, and the kind of life each city supports. We do not rank cities against each other with a score, because the weighting of those factors is yours, not ours.
How we keep it current
Immigration routes, thresholds and fees are re-verified every three months, and immediately whenever we learn of a change. Practical guides and cost estimates every six months. Corporate and legal pages every twelve months, and whenever a provider changes.
When a guide falls out of date it is marked Needs Update, which removes it from search results until a person has re-checked it. We would rather be temporarily invisible than reliably wrong.
What this method cannot do
- It cannot tell you whether you qualify for anything. Immigration rules are applied case by case.
- It cannot turn a published processing time into a promise. Authorities state targets, not guarantees.
- It cannot keep pace with rental markets in Madrid and Barcelona, where published data lags reality.
- It cannot replace a lawyer or a gestor you have hired to look at your specific situation.
Official sources
Every factual claim on this page was checked against these primary documents.