Form A1: Secondment and activity in several countries, what the Cleiss says

Form A1 is a certificate that indicates which social security legislation applies to you when you are in a situation of European mobility (EU, EEA, Switzerland). It is particularly relevant for posted workers whose initial assignment is a maximum of 24 months in an EU or EEA country or in Switzerland, and for workers who work in several countries. The Cleiss (Centre for European and International Social Security Liaison) clarifies that it does not issue this document itself under any circumstances.

This page is based solely on the Cleiss pages consulted on 18/10/2026. It does not detail the application procedure, contributions or penalties: these points should be checked with the Urssaf or the Cleiss before any decision.

What is form A1?

Its official name, according to the Cleiss, is: "Certificate concerning the social security legislation applicable to the holder." The Cleiss explains that it serves "to certify your social security status" and that it is intended for people in situations of European mobility.

According to Cleiss, it concerns travel within the EU, the EEA, and Switzerland. In other words, it documents a specific point: which social security scheme you fall under during the period in question.

Who issues it in France?

Cleiss writes: "Under no circumstances is Cleiss competent to issue form A1." The application process is not detailed here: it is carried out with the organization concerned.

Secondment: remain under the system of your usual country of employment

The Cleiss defines posting as "the act of maintaining a worker under the social security system of their usual country of employment." Within the EU, the EEA, and Switzerland, the A1 form is the document that certifies this situation. For a country linked to France by a social security agreement, the Cleiss cites a different document, the SE form, and not the A1.

The indicated durations

The Cleiss adds that "these periods may be extended in certain states and under certain conditions." The conditions are not detailed on the pages consulted.

The case of countries without an agreement with France and that of the United Kingdom are not covered here: see the Cleiss Secondment FAQ.

An example outside the EU: Monaco

Monaco is neither in the EU, nor the EEA, nor Switzerland. This case falls under a bilateral agreement, and the Cleiss website does not refer to the form as A1. For an employee of a company established in Monaco who works in France, Cleiss indicates that the employer maintains them under the Monegasque social security system, "as permitted by the bilateral agreement." Since April 1, 2017, the form certifying the applicable social security legislation "must be made available to the inspection authorities.".

According to the summary published by Cleiss, the Franco-Monegasque social security convention sets out the starting rule (art. 3): the applicable legislation is that of the State where the salaried activity is carried out, with exceptions, in particular for posted workers.

Operating in multiple countries: one single regime

For the employer, Cleiss sets out the following principle: an employee who usually carries out his activities in several EU, EEA and Swiss states "must be covered by a single social security scheme".

Which institution decides? The Cleiss writes that "it is up to the competent body in their state of residence to determine which social security scheme they should be affiliated to." Its page for employers follows a question-and-answer approach:

1. The institution of the employee's state of residence examines his situation.
2. She asks: "Is a substantial part of its business conducted in that state?"«
3. If not, you need to know where the company's headquarters or those of other employers are located.
4. The employee is then provided with document A1.

The Cleiss specifies that "all employees with multiple jobs must have this document." The employee must contact the relevant institution in their country of residence for the necessary formalities. In France, the Urssaf is responsible for collecting social security contributions.

The Cleiss employers' page does not quantify the "substantial share": it refers to Article 14, § 8 of Regulation (EC) No 987/2009 for its definition. Therefore, no threshold is published here.

Form A1: What changes depending on your case

• Seconded employee or employee with multiple employers The A1 form does not certify the same thing. In the first case, it certifies continued application of the social security system of the country of habitual employment. In the second, it establishes a single system for all activities.
• Destination : 24 months maximum for the EU, EEA and Switzerland (case of A1); between 1 and 5 years for countries linked to France by an agreement (Cleiss cites the SE form).
• Professional status : the competent body in France varies (Urssaf, MSA, Enim).
• Manager, self-employed worker, mixed situation Not addressed here. The rule depends on your situation and should be verified before making a decision.
• Taxation The A1 form certifies compliance with applicable social security legislation (Cleiss). This page does not deal with taxation; this must be verified separately.

No results are promised.

Form A1: numerical example (fictitious profile)

Situation. Marc, 41, an executive at a company based in Lyon, is due to work in another EU state from March 1, 2027. This data is based on assumptions in the fictitious profile.

Issue. He wants to know the maximum initial period of 24 months during which he can remain affiliated with the French social security system. He's worried about missing a deadline.

Strategy. He starts with the Cleiss rule: an initial maximum duration of 24 months in the EU, EEA, or Switzerland. Counting 24 full months from March 1, 2027, the calculation is straightforward. The pages consulted do not detail the calculation of the last day. He notes that Urssaf is the organization cited by Cleiss for employers, and he indicates the deadline.

Result. The 24 full months end on February 28, 2029, which is 731 calendar days, as 2028 is a leap year. An extension remains possible "in certain states and under certain conditions" (Cleiss): no date is calculated beyond that.

This profile is fictitious. The dates illustrate the calculation. They do not predict your situation.