Belgian law firm Tiberghien has issued an alert on 22 January detailing the business impact of a 11 December 2025 judgment of the European Court of Justice that quietly rewrites how companies must calculate the so-called 25 % rule under EU social-security Regulation 883/2004. The case involved a Swiss-based employee resident in Germany whose duties were split between Switzerland, Germany and multiple non-EU jurisdictions.
Until now, many Belgian employers assumed that only work performed inside the EU/EEA (plus Switzerland) counted toward the 25 % threshold that determines whether the employee falls under the social-security system of the home state. The ECJ has clarified that *all* remunerated activity worldwide — even days worked in third countries such as the United States, India or the UAE — must be included in the numerator. As a result, mobile staff who spend significant time on long-haul assignments may unexpectedly exceed the 25 % mark, shifting social-security liability back to their country of residence, typically Belgium.
For companies running Belgian payrolls, the widened definition raises immediate compliance questions: Should salary split arrangements be re-engineered? Are shadow payrolls required in multiple jurisdictions? Will retroactive employer and employee contributions be due if the wrong system has been applied? Tiberghien recommends an urgent audit of travel-time records, secondment agreements and cost-allocation models, particularly for executives who mix EU remote work with global site visits.
![ECJ ruling expands 25 % ‘substantial activity’ test for Belgian cross-border staff]()
In parallel with any payroll or legal review, companies may benefit from working with travel-documentation specialists. VisaHQ’s Belgium platform (https://www.visahq.com/belgium/) streamlines the procurement of visas, work permits and other entry authorisations worldwide, providing real-time rule changes and centralised tracking that dovetail neatly with social-security audits. Using such a service helps ensure that internationally mobile staff remain immigration-compliant while employers capture accurate data for the broadened 25 % calculation.
The judgment also dovetails with the post-pandemic surge in ‘work-from-anywhere’ policies. Belgian tax authorities already enforce strict limits on cross-border telework; the ECJ decision makes it harder to ring-fence offshore days from social-security exposure. Failure to adapt could trigger dual coverage, administrative fines and the loss of Belgian benefits for employees. Multinationals are advised to update internal guidelines, brief travelling staff and liaise with host-country advisers to leverage bilateral waivers where available.
Although the ruling stems from a Swiss-German dispute, its reasoning applies EU-wide and is therefore binding on Belgian competent authorities. The message for HR and mobility teams is clear: the 25 % rule is no longer an EU-only calculation — global days now count, too.
Until now, many Belgian employers assumed that only work performed inside the EU/EEA (plus Switzerland) counted toward the 25 % threshold that determines whether the employee falls under the social-security system of the home state. The ECJ has clarified that *all* remunerated activity worldwide — even days worked in third countries such as the United States, India or the UAE — must be included in the numerator. As a result, mobile staff who spend significant time on long-haul assignments may unexpectedly exceed the 25 % mark, shifting social-security liability back to their country of residence, typically Belgium.
For companies running Belgian payrolls, the widened definition raises immediate compliance questions: Should salary split arrangements be re-engineered? Are shadow payrolls required in multiple jurisdictions? Will retroactive employer and employee contributions be due if the wrong system has been applied? Tiberghien recommends an urgent audit of travel-time records, secondment agreements and cost-allocation models, particularly for executives who mix EU remote work with global site visits.
In parallel with any payroll or legal review, companies may benefit from working with travel-documentation specialists. VisaHQ’s Belgium platform (https://www.visahq.com/belgium/) streamlines the procurement of visas, work permits and other entry authorisations worldwide, providing real-time rule changes and centralised tracking that dovetail neatly with social-security audits. Using such a service helps ensure that internationally mobile staff remain immigration-compliant while employers capture accurate data for the broadened 25 % calculation.
The judgment also dovetails with the post-pandemic surge in ‘work-from-anywhere’ policies. Belgian tax authorities already enforce strict limits on cross-border telework; the ECJ decision makes it harder to ring-fence offshore days from social-security exposure. Failure to adapt could trigger dual coverage, administrative fines and the loss of Belgian benefits for employees. Multinationals are advised to update internal guidelines, brief travelling staff and liaise with host-country advisers to leverage bilateral waivers where available.
Although the ruling stems from a Swiss-German dispute, its reasoning applies EU-wide and is therefore binding on Belgian competent authorities. The message for HR and mobility teams is clear: the 25 % rule is no longer an EU-only calculation — global days now count, too.
