Article 13, §1 of Regulation 883/2004 of the European Parliament and of the Council of 29 April 2004 on the coordination of social security systems states that a person who normally pursues an activity as an employed person in two or more member states shall be subject to:
- the legislation of the member state of residence if he/she pursues a substantial part of his/her activity in that member state or if he/she is employed by various undertakings or various employers whose registered office or place of business is in different member states, or
- the legislation of the member state in which the registered office or place of business of the undertaking or employer employing him/her is situated, if he/she does not pursue a substantial part of his/her activities in the member state of residence.
Article 14, §8 of Regulation No 987/2009 of the European Parliament and of the Council of 16 September 2009 laying down the procedure for implementing Regulation No 883/2004 on the coordination of social security systems further clarifies that a “substantial part of the employee’s activity” pursued in a member state shall mean a quantitatively substantial part of all the activities of the employed person pursued there, without this necessarily being the major part of those activities. This article provides indicative criteria in order to determine whether a substantial part of the activities is pursued in a member state, being the employee’s working time and/or remuneration. In the framework of an overall assessment, a share of less than 25 % in respect of the criteria mentioned above shall be an indicator that a substantial part of the activities is not being pursued in the relevant member state.
The Dutch translation of article 14, §8 of Regulation No 987/2009 refers to the employee’s working time and/or remuneration being “inter alia / also” (“mede” in Dutch) indicative criteria in order to determine whether a substantial part of the activities is pursued in a member state. According to the Supreme Court of the Netherlands (“Hoge Raad der Nederlanden”), it follows indisputably from the use (in the Dutch language version of article 14, §8 of Regulation No 987/2009) of the terms “mede” (“inter alia / also”) and “indicatieve criteria” (“indicative criteria”) and of the noun “indicatie” (“indicator”) that, if the employee’s working time and/or remuneration in the member state of residence represent less than 25 % of those criteria envisaged for all the employee’s activities in the various member states, there is a possibility of taking into account other circumstances in an overall assessment of that employee’s situation.
In its judgement of 4 September 2025 in case C-203/24 (KN v. Raad van bestuur van de Sociale verzekeringsbank), the Court of Justice of the European Union clarified the criteria for determining if a person working in multiple member states carries out a substantial part of their activity in their member state of residence, reaffirming its previous interpretation.
Here are three takeaways of this judgement:
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Ascertain whether 25% of working time and/or remuneration is performed respectively obtained in the member state of residence
It is for the competent social security institution to ascertain, in the context of an overall assessment of an employee’s situation, whether at least 25 % of his/her working time and/or remuneration is performed respectively obtained in the member state of residence.
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Other circumstances or criteria are not taken into consideration
The Court of Justice of the European Union clarifies that for Article 14, §8 of Regulation No 987/2009, only working time and/or remuneration are considered when determining if an employee performs a substantial part of their activity in their member state of residence, despite potentially ambiguous language in the Dutch version. Other factors are not taken into account.
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Assessment should take into account the employee’s projected situation for the following 12 calendar months
To assess if an employee working in multiple member states carries out a substantial part of their activity in their country of residence, consider the projected situation for the next 12 calendar months starting from when the cross-border work begins.
Want to know more?
With increasing internationalisation in both society and the workplace, employers are increasingly encountering situations of cross-border employment. Correctly and thoroughly assessing which country’s social security legislation will be applicable is indispensable for employers planning to engage employees in a cross-border setting. If you would like to be assisted in this assessment, our Employment team is ready to assist you.