openaccountants EU Social Security Coordination
General reference only. This skill is general tax/accounting reference material for AI-assisted workflows. It has not been reviewed for any specific person's facts, documents, elections, deadlines, residency, filing status, or local procedures. Do not rely on it to file, pay, amend, or take a tax position without review by a qualified professional in the relevant jurisdiction.
Skill Metadata
| Field | Value |
|---|---|
| Jurisdiction | EU-27, EEA (Iceland, Liechtenstein, Norway), Switzerland, UK (via TCA) |
| Primary Legislation | Regulation (EC) No 883/2004 on the coordination of social security systems |
| Implementing Legislation | Regulation (EC) No 987/2009 laying down the procedure for implementing Reg 883/2004 |
| Key CJEU Rulings | C-743/23 (Sep 2025, "substantial part" calculation); C-694/20 (Dec 2022); C-610/18 (2020, AFMB) |
| Scope | Determination of applicable social security legislation for persons active in multiple member states |
| Contributor | OpenAccountants |
| Validation Date | May 2026 |
| Skill Version | 1.0 |
Section 1 — Core principle: you pay social security in ONE country only
Article 11(1) of Regulation 883/2004:
"Persons to whom this Regulation applies shall be subject to the legislation of a single Member State only."
This is the foundational rule. A person working across EU/EEA borders pays social security contributions in exactly one country. They cannot be required to pay in two countries simultaneously. The entire purpose of Regulation 883/2004 is to determine which single country's legislation applies.
What "social security" covers under the Regulation
The Regulation coordinates ALL branches of social security (Article 3):
| Branch | Examples |
|---|---|
| Sickness benefits | Health insurance, sick pay |
| Maternity and equivalent paternity benefits | Parental leave payments |
| Invalidity benefits | Disability payments |
| Old-age benefits | State pension |
| Survivors' benefits | Widow/widower pension |
| Benefits in respect of accidents at work and occupational diseases | Work injury insurance |
| Death grants | Funeral payments |
| Unemployment benefits | Jobseeker's allowance |
| Pre-retirement benefits | Early retirement schemes |
| Family benefits | Child benefit |
It does NOT cover social assistance, supplementary pension schemes governed by contract, or special non-contributory cash benefits (which are listed in Annex X and non-exportable).
Four principles of coordination
- Single applicable legislation — you pay in one country only
- Equal treatment — same rights and obligations as nationals of the country where you're covered
- Aggregation — periods of insurance in other countries count toward benefit entitlements
- Exportability — cash benefits can generally be paid regardless of which country you live in
Section 2 — Determination rules: lex loci laboris
General rule (Article 11(3)(a)): The legislation of the member state where the person is employed or self-employed applies. This is the "lex loci laboris" (law of the place of work) principle.
| Situation | Applicable Legislation | Article |
|---|---|---|
| Employed in one member state | State where employed | Art 11(3)(a) |
| Self-employed in one member state | State where self-employed | Art 11(3)(a) |
| Civil servant | State of the employing administration | Art 11(3)(b) |
| Receiving unemployment benefits | State providing the benefit | Art 11(3)(c) |
| Called up for military/civil service | State requiring the service | Art 11(3)(d) |
| No activity (economically inactive) | State of residence | Art 11(3)(e) |
The general rule is simple: you work in country X, you pay social security in country X. Complications arise only when a person works in multiple countries, is posted abroad, or combines employment and self-employment across borders.
What "employed" means
The Regulation uses the definition of the member state whose legislation is being determined. A person is considered employed or self-employed based on the national law of the relevant member state. There is no EU-wide definition of employment vs self-employment for SS purposes.
Section 3 — Posted worker exception (A1 certificate)
Article 12 of Regulation 883/2004:
An employer may send (post) a worker to another member state while keeping that worker subject to the home country's social security legislation, provided:
| Condition | Requirement |
|---|---|
| Duration | Maximum 24 months (anticipated duration at outset) |
| Replacement prohibition | The posted worker must not be sent to replace another posted worker whose posting period expired |
| Prior insurance | The worker must have been subject to the legislation of the sending state immediately before the posting began |
| Direct relationship | The worker must remain under the authority of the sending employer during the posting |
| Employer's substantial activity | The employer must normally carry out substantial activities in the sending state (not merely internal management) |
Key limitations
- The 24-month limit is strict. If the posting is expected to exceed 24 months from the outset, Article 12 does NOT apply.
- If circumstances change and the posting extends beyond 24 months, an Article 16 agreement (exceptional agreement between competent institutions) can be requested.
- The worker must have been insured in the sending state BEFORE the posting. You cannot hire someone specifically to post them on day one (though a minimum prior period is not specified in the Regulation, national authorities typically require at least 1 month).
- The employer must have genuine, substantial business activity in the sending state. A letterbox company with no real activity cannot post workers.
A1 certificate for posted workers
The A1 certificate (Portable Document A1) is the proof that a posted worker remains subject to the sending state's legislation. It is issued by the sending state's competent institution.
Until an A1 certificate is obtained, the host country can demand contributions. The A1 certificate is binding on the host country's institutions and courts (CJEU: A-Rosa Flussschiff, C-620/15) — the host country cannot refuse to accept a valid A1 unless it has been withdrawn or invalidated through the official dispute procedure.
Section 4 — Multi-state workers (Article 13)
A person who normally pursues activity in two or more member states simultaneously follows different determination rules.
Employed persons in two or more states (Article 13(1))
| Test | Result |
|---|---|
| Pursues substantial part (≥ 25%) of activity in residence state | Residence state's legislation applies |
| Does NOT pursue substantial part in residence state, employed by ONE employer | Employer's registered office state applies |
| Does NOT pursue substantial part in residence state, employed by TWO+ employers in same state | That state's legislation applies |
| Does NOT pursue substantial part in residence state, employed by TWO+ employers in different states (one of which is residence) | Employer state (other than residence) applies |
| Does NOT pursue substantial part in residence state, employed by TWO+ employers all in states other than residence | Residence state's legislation applies |
The 25% substantial activity test
Article 14(8) of Implementing Regulation 987/2009:
"Substantial part" means a quantitatively substantial part of all activities — measured by:
- Working time (hours/days worked in the state as a share of total working time), AND/OR
- Remuneration (pay attributable to work in the state as a share of total pay)
The 25% threshold: If LESS than 25% of either working time or remuneration is in the residence state, a substantial part is NOT being pursued there.
CJEU ruling C-743/23 (September 2025): Confirmed that:
- The 25% threshold is assessed based on the projected situation over the next 12 months from the start of multi-state activity
- Only working time and remuneration are relevant criteria — nature of work, location of clients, or other factors are irrelevant
- The assessment includes work in third countries (non-EU) in the denominator when calculating the percentage
Determination procedure (Article 16 of Reg 987/2009)
- The worker (or employer) notifies the competent institution of the residence state
- The residence state provisionally determines applicable legislation
- The residence state informs all other states' institutions within 2 months
- If no objection within 2 months → determination becomes definitive
- If objection → dialogue between institutions; if no agreement within 6 months → refer to Administrative Commission
During the provisional period, the worker is subject to the provisionally determined legislation. This avoids gaps in coverage.
Section 5 — Self-employed across borders (Article 13(2))
| Test | Result |
|---|---|
| Pursues substantial part (≥ 25%) of self-employed activity in residence state | Residence state's legislation applies |
| Does NOT pursue substantial part in residence state | State where the centre of interest of activities is situated |
Centre of interest determination
For self-employed persons not meeting the 25% threshold in their residence state, the "centre of interest" is determined by considering:
- Where the fixed and permanent premises for the activity are located
- The habitual nature or duration of activities pursued
- The number of services rendered
- The intention of the person as revealed by all circumstances
Practical example: A freelance consultant resident in Belgium who works 60% of the time at clients in the Netherlands and 40% in Belgium → 40% ≥ 25% in residence state → Belgium's legislation applies.
Practical example: A freelance developer resident in Portugal who works 90% for clients accessed remotely from Portugal but the registered business is in Estonia → work is performed in Portugal (≥ 25%) → Portugal's legislation applies.
Section 6 — Simultaneous employment and self-employment (Article 13(3))
Rule: A person who normally pursues employment in one state AND self-employment in another state is subject to the legislation of the state where the employed activity is pursued.
| Combination | Applicable Legislation |
|---|---|
| Employed in state A + self-employed in state B | State A (employment state) |
| Employed in states A and B + self-employed in state C | Determined per Article 13(1) rules for multi-state employees |
Key consequence: A person employed in Germany who also freelances for clients in France pays ALL social security (including on the freelance income) in Germany. France cannot claim contributions on the self-employed activity.
Exception: If the person pursues employed activity in two or more states AND self-employment in one or more states, the multi-state employee rules of Article 13(1) determine the applicable legislation first, and then that legislation covers ALL activities.
Section 7 — A1 certificate: what it is, how to get it, who issues it
What the A1 certificate is
The Portable Document A1 (PD A1) is an official certificate confirming which member state's social security legislation applies to a person. It is proof that the holder does not need to pay contributions in any other member state.
When you need an A1 certificate
| Situation | A1 needed? |
|---|---|
| Posted to another member state for up to 24 months | YES — mandatory before posting begins |
| Normally working in two or more member states | YES — to confirm which legislation applies |
| Self-employed temporarily performing activity in another state | YES — mandatory |
| Business trip (< 2 days, no work performed) | NO — but advisable for evidence |
| Attending a conference or training | Generally NO — but complex if any "work" is performed |
How to obtain an A1 certificate
- Application: Submit to the competent institution of the state whose legislation you claim applies
- Information required: Identity details, employer details, nature of activity, countries of activity, anticipated duration, percentage of activity per country
- Processing time: Varies by country (1–8 weeks typically)
- Validity: Covers the period specified; for multi-state workers, typically issued for up to 24 months and renewable
- Retroactive issue: Can be issued retrospectively (but some countries resist this; apply BEFORE activity begins)
Issuing authority by country
| Country | Competent Institution for A1 |
|---|---|
| Germany | GKV-Spitzenverband (DVKA) / competent Krankenkasse |
| France | URSSAF / CPAM (depends on scheme) |
| Netherlands | SVB (Sociale Verzekeringsbank) |
| Belgium | RSZ/ONSS (employed) / RSVZ/INASTI (self-employed) |
| Italy | INPS (Istituto Nazionale della Previdenza Sociale) |
| Spain | TGSS (Tesorería General de la Seguridad Social) |
| Portugal | ISS (Instituto da Segurança Social) |
| Austria | ÖGK (Österreichische Gesundheitskasse) |
| Ireland | Dept of Social Protection, Scope Section |
| Poland | ZUS (Zakład Ubezpieczeń Społecznych) |
| Sweden | Försäkringskassan |
| Denmark | Udbetaling Danmark |
| Malta | Department of Social Security |
| Greece | EFKA (e-EFKA electronic system) |
| Finland | ETK (Finnish Centre for Pensions) |
Consequences of not having an A1
- Host country may demand contributions (and the worker/employer cannot refuse)
- If contributions are paid in the wrong country, refund procedures apply but take 12–24 months
- Penalties possible in some countries for working without a valid A1 (especially France: fines for employer)
- The worker remains covered by the correct legislation regardless of whether the A1 exists — the certificate is declaratory, not constitutive
Section 8 — EEA/Switzerland extension
Regulation 883/2004 applies to:
| Territory | Basis |
|---|---|
| EU-27 member states | Directly applicable EU regulation |
| Iceland, Liechtenstein, Norway | EEA Agreement (Decision of the EEA Joint Committee No 76/2011) |
| Switzerland | EU-Switzerland Agreement on the Free Movement of Persons (in force 1 June 2002) |
The rules apply identically. A person working in Germany and Switzerland follows the same Article 13 determination as a person working in Germany and France.
Limitation: The coordination only works within the EU/EEA/CH block. A person working in Germany and the United States is NOT covered by Regulation 883/2004 for the US portion — a bilateral totalization agreement between Germany and the US (if one exists) governs that relationship.
Section 9 — UK post-Brexit (Trade and Cooperation Agreement)
Legal basis
The EU-UK Trade and Cooperation Agreement (TCA), signed 30 December 2020, contains a Protocol on Social Security Coordination that provides continued coordination for persons moving between the EU and the UK after 1 January 2021.
Who is covered
| Persons | Coverage |
|---|---|
| Persons covered by the Withdrawal Agreement | Continue under the WA (more comprehensive rights) |
| Persons NOT covered by the WA who move between EU and UK after 1 Jan 2021 | Covered by TCA Protocol |
| Third-country nationals moving between EU and UK | Generally NOT covered by TCA Protocol (unlike Reg 883/2004 which covers all nationalities) |
Key TCA rules (similar to but narrower than Reg 883/2004)
| Rule | TCA Provision |
|---|---|
| Single applicable legislation | Article SSC.10 — same principle as Art 11 of 883/2004 |
| Lex loci laboris | Article SSC.10(3) — same general rule |
| Posted workers | Article SSC.11 — maximum 24 months (same as Art 12) |
| Multi-state workers | Article SSC.12 — similar to Art 13 (25% test applies) |
| A1-equivalent certificate | PDA1 certificate issued under TCA provisions |
Key differences from Reg 883/2004
| Difference | Impact |
|---|---|
| No aggregation for unemployment in some cases | UK workers moving to EU may not aggregate UK periods for unemployment benefit |
| Healthcare limited | No EHIC for new cases; S1 for pensioners continues |
| Family benefits limited | No export of family benefits in all cases |
| Nationality restriction | TCA covers EU and UK nationals (not all nationalities like 883/2004) |
| No planned revision process | Unlike 883/2004 which has an ongoing revision proposal |
Practical guidance for UK-EU cross-border workers
- A UK national posted from the UK to France: TCA Art SSC.11 applies → A1-equivalent from HMRC → continue UK NIC for up to 24 months
- A UK company hiring a remote worker in Spain: Worker is subject to Spanish SS → employer registers with Spanish TGSS
- A freelancer resident in UK working 50% UK / 50% Germany: TCA Art SSC.12 → substantial part in UK (50% ≥ 25%) → UK NIC applies to all activity
Section 10 — Common scenarios with worked examples
Scenario A — Remote worker for foreign employer
Facts: Maria lives in Portugal. She is employed full-time by a German company (GmbH). She works 100% remotely from her home in Lisbon. She never travels to Germany.
Analysis:
- Maria pursues activity in ONE state only (Portugal — where work is physically performed)
- Article 11(3)(a) applies: legislation of the state where employed = Portugal
- Maria is subject to Portuguese social security
- German employer must register as employer with Portuguese ISS and pay Portuguese contributions
Result: Portugal. The German employer registers with ISS, pays employer/employee contributions per Portuguese rates.
Scenario B — Posted worker
Facts: Johann works for a Munich-based engineering firm. He is sent to oversee a construction project in Austria for 18 months. He will return to Munich afterwards.
Analysis:
- Article 12 posting rules apply
- Duration: 18 months < 24 months maximum ✓
- Johann was previously insured in Germany ✓
- Employer has substantial activity in Germany ✓
- Not replacing another posted worker ✓
Result: Germany continues to apply. Employer obtains A1 from GKV-Spitzenverband (DVKA). Johann does NOT pay Austrian social security.
Scenario C — Multi-country freelancer
Facts: Sophie is a freelance UX designer resident in Belgium. She works 30% of her time for clients in Belgium, 40% in the Netherlands, and 30% in France.
Analysis:
- Article 13(2) for self-employed in multiple states
- Does Sophie pursue a substantial part in her residence state (Belgium)? 30% ≥ 25% → YES
- Belgium's legislation applies to ALL of Sophie's self-employed activity
Result: Belgium. Sophie pays Belgian self-employed social security (RSVZ/INASTI) on her entire worldwide self-employed income. No contributions owed in NL or FR.
Scenario D — Employee plus freelancer in different countries
Facts: Marco is employed in Italy (full-time software engineer at an Italian company). He also freelances as a consultant for German clients, performing this work from his home in Italy.
Analysis:
- Article 13(3): employed + self-employed in different states
- Employed activity in Italy → Italy's legislation applies to ALL activity
- BUT: the freelance work is ALSO performed in Italy (from home) → this is actually a single-state case
- Italy's legislation applies regardless
Result: Italy. INPS contributions on both employed and self-employed income. No German obligation.
Scenario E — UK employee working partly in EU post-Brexit
Facts: James is a UK resident employed by a UK company. He works 3 days/week from London (60%) and 2 days/week from the company's Paris office (40%).
Analysis:
- TCA Protocol Art SSC.12 (multi-state worker)
- James is resident in UK. Does he pursue ≥ 25% in UK? 60% ≥ 25% → YES
- UK legislation applies to all activity
Result: UK. James pays UK NIC on all earnings. French contributions not owed. Employer obtains PDA1 from HMRC confirming UK coverage.
PROHIBITIONS
- NEVER tell a user they must pay social security in two EU/EEA countries simultaneously. The fundamental principle is single applicable legislation.
- NEVER assume that the country where a person is resident is automatically the competent SS state. Lex loci laboris means the country of WORK generally applies.
- NEVER advise that an A1 certificate is "optional" or "nice to have." For posted workers and multi-state workers, it is the essential proof document.
- NEVER assume Regulation 883/2004 applies to non-EU/EEA/CH countries. For US, Canada, Australia, etc., bilateral totalization agreements (if they exist) govern.
- NEVER compute contribution amounts. This skill determines WHICH country — the country skill provides the rates and computation.
- NEVER advise creating artificial posting arrangements to avoid higher contributions in the host state. This is a known abuse pattern and authorities actively investigate it.
Disclaimer
This skill and its outputs are provided for informational and computational purposes only and do not constitute tax, legal, or financial advice. Open Accountants and its contributors accept no liability for any errors, omissions, or outcomes arising from the use of this skill. Social security coordination determinations are fact-specific and have significant financial consequences. All outputs must be reviewed and signed off by a qualified social security coordination specialist before acting upon.
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