US Expats Moving Across Europe: Tax, Pensions & Social Security

Globally mobile professionals collect countries the way other careers collect employers - a posting here, a promotion there, a family decision in between. Each move rewires how two systems tax the same salary, the same pension pot and the same Social Security record, and the rewiring is never the same twice.

This article is aimed at US citizens and green-card holders who have lived or expect to live in two or more of France, Switzerland, Portugal and the Netherlands, and at the professionals who advise them. It sets the four treaties and four totalization agreements side by side - as quoted texts, with their gaps stated - and leaves each country's full mechanics to the country deep-dives.

This article describes how United States federal tax law and the relevant income tax treaties and totalization agreements apply to US persons. It summarises French, Swiss, Portuguese and Dutch rules only as published by each country's tax and social security authorities, for context, and is not French, Swiss, Portuguese or Dutch tax, legal or succession advice - those questions belong with a professional qualified in the relevant country.

Each treaty and each totalization agreement stands alone

The United States has income tax treaties with each of the four countries and social security totalization agreements with thirty countries, the four included. Every one of those instruments is bilateral: it binds the United States and one partner, on its own text. There is no European average, no master treaty, and no rule that what one treaty settles another even mentions.

The bilateral point has a sharp totalization consequence. Each agreement's totalization article counts US periods together with that partner's periods - the French agreement counts French credits, the Swiss agreement Swiss ones, and so on, each requiring at least six US quarters of coverage. Whether periods from two or more partner countries can be combined in a single US computation is a question none of the located Social Security Administration materials answers - the program manual sections and handbook reviewed for this series address only the bilateral case. This article records that absence rather than asserting an answer in either direction: a multi-country contribution record is a question to put to the SSA and your advisers with the actual record in hand.

One reassurance is common to the agreements as the SSA describes them: counting is not transferring. In the pamphlet wording used for several of these agreements, "your credits are not actually transferred from one country to the other. They remain on your record in the country where you earned them" - each country pays its own, sometimes pro-rated, benefit from its own record.

Four treaties, four pension patterns: the side-by-sidetable

Private-pension allocation is where the four treaties diverge most instructively. France allocates to the source state and protects that allocation from the US saving clause; Switzerland and Portugal allocate to the residence state without protection; the Netherlands allocates to the residence state, adds a source-state right over certain lump sums - and its saving-clause exceptions list could not be retrieved at all. The table quotes each text's operative fragment.

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Three disciplines follow from the table - which is a dated reading of the four texts as officially published, verified in August–September 2026, not a standing rating of any treaty. First, never transplant: each treaty is read on its own text, and an analysis correct in Paris can be wrong in Geneva. Second, the gaps are part of the law as located: for the Netherlands, every end-to-end double-tax outcome in this series is presented as the professionals' computation because the relief and saving-clause articles could not be retrieved. Third, social security has its own four-way split - France's treaty rule, Switzerland's 15% source cap, Portugal's non-exclusive "may be taxed", the Netherlands' paying-state-exclusive text - each covered in its country's pieces.

Certificates of coverage and the five-year pattern

On the contributions side, each posting runs on paper. When an agreement assigns your work to one country's system, the covering country documents it: in the SSA's words, a US Certificate of Coverage" serves as proof that the employee and employer are exempt from the payment of Social Security taxes to the foreign country." All four agreements share the detached-worker pattern for assignments not expected to exceed five years.

US certificates are requested from the Social Security Administration - online through its certificate service or through its Baltimore international office - and each partner country issue sits own: the SSA's pamphlets name form SE-404-1/SE-404-2 for France, CH/USA 10for Switzerland and P/USA 1 for Portugal, with the Dutch process described in the Netherlands pamphlet. A professional who has moved twice should expect to have held more than one certificate, from more than one issuer, over a career.

Self-employment is the trap inside the pattern, because the assignment rule is not uniform. Under the Swiss, Portuguese and Dutch agreements, as the SSA pamphlets state them, a self-employed person is covered where they reside. The French agreement works differently: assignment follows where the work is performed and, for activity in both countries, the principal activity - with a two-year rule for a businessactivity transferred temporarily. A consultant who crosses one of these borders mid-career should not assume the old rule travelled with them.

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What your vehicles do when you leave

Local savings vehicles are built by local law, and local law decides what happens to them at departure. The four countries answer differently, this series holds verified answers for only some of the cases, and where a rule is not held the honest output is a question for the named professional rather than a borrowed answer.

Two rules are held and worth quoting. Switzerland: on leaving for good, the compulsory part of an occupational-pension termination benefit "cannot be paid out in cash" if you move to an EU or EFTA state - it goes to a vested-benefits account - while a move to the United States sits outside that restriction, so cash payment of the full termination benefit is permissible under the published framework. France: a PEA may generally be kept after leaving France - the plan must be closed only on transfer to a non-cooperative jurisdiction - with the plan's rules continuing to apply. By contrast, what a Portuguese savings product or a Dutch lijfrente does on emigration is not held in this series' fact base: those are questions for a contabilista certificado or a belastingadviseur, asked before the move rather than after. And every vehicle, moved or kept, stays on the US reporting stack throughout.

When residence starts and stops: four different clocks

The four countries do not even agree on what a tax year of arrival looks like. Portugal runs a statutory clock: residence generally begins after more than 183 days, consecutive or not, in any 12-month period beginning or ending in the year - or from a dwelling suggesting habitual residence - and its split-year rule starts residence on the first day of the qualifying stay.

France and Switzerland assess by criteria rather than one count: France by foyer, principal place of stay, professional activity or centre of economic interests; Switzerland by domicile with intent to remain, or a qualified stay with published day thresholds. The Netherlands is the most open-textured of the four — residence is assessed on the facts and circumstances, with no fixed statutory day count located in this series' sources, and the migration year is filed on its own return form. The hub article on moving between the four countries carries the side-by-side table; the point here is only that the clock you leave is never the clock you arrive on.

Overlap years deserve their own respect. A move in May can leave you inside two countries' definitions at once for part of a year, with the treaty tie-breaker as the referee and a migration-year filing on at least one side - Portugal's split-year rule, the Dutch M form, and the French and Swiss arrival practices each handled in the country pieces. The US return, meanwhile, simply continues: a citizen files Form 1040 on worldwide income in a moving year like any other, with the automatic two-month extension available to taxpayers abroad on the regular due date. The one habit that survives every move is filing everywhere you must, on each system's own clock.