The A1 certificate: one form that decides where you pay contributions

The Commission's Your Europe forms table defines it in one line: the A1 is the statement of applicable legislation — useful to prove that you pay social security contributions in another EU country, as a posted worker or while working in several countries at the same time. It is issued by the social security institution of the country where you are insured; if you are posted, that is the institution in the sending country.

That's why site inspectors and host-country authorities ask for it: the A1 is the paper that answers "why is this worker not paying into our system?"

Source: Your Europe — Useful forms for social security rights (European Commission), read 8 September 2026.

The A1 exists because of the coordination regulation's core principle. Article 11 of Regulation (EC) 883/2004 states that persons to whom the regulation applies shall be subject to the legislation of a single Member State only. You are never supposed to owe contributions in two systems for the same work — the whole game is determining which single system applies, and the A1 is the certificate of that determination.

Source: Regulation (EC) No 883/2004, Article 11 — EUR-Lex, read 8 September 2026.

Article 12 of the same regulation sets the posting rule: an employee posted by their employer to another member state continues to be subject to the legislation of the first Member State, provided that the anticipated duration of such work does not exceed twenty-four months and that he is not sent to replace another person. The self-employed have a parallel rule for temporarily pursuing a similar activity abroad.

Read the two conditions literally: a posting planned to run past 24 months doesn't qualify, and neither does rotating workers into the same post to reset the clock — the no-replacement condition exists precisely for that.

Source: Regulation (EC) No 883/2004, Article 12 — EUR-Lex, read 8 September 2026.

The A1 settles contributions, not treatment. Per the Commission's guidance for posted workers who move to the posting country, the healthcare paper is the S1 form — requested from your health insurance institution at home and handed to the local health insurance institution where you'll be working, entitling you and your family to healthcare during the residence abroad. We cover the S1, S2 and the rest of the family in our coordination guide.

And neither form is private cover: postings that come with visa or landlord requirements for insurance still need a policy — which is the part we arrange.

Source: Your Europe — Health insurance cover when living abroad, read 8 September 2026.