Tax and social security do not read the same calendar. Tax counts days — the 34 of the tolerance. Social security counts a percentage of working time, and switching over there carries heavier consequences: the question is not where part of the salary is taxed, but which scheme covers you — healthcare, unemployment, pension — and where the employer pays contributions, on the whole salary.
The basic rule: 25 %
The European coordination regulation sets the principle: an employee who carries out a substantial part of their activity in their country of residence — at least 25 % of working time or of remuneration — comes under the social security system of their country of residence, not that of the employer's country.
For a full-time job, 25 % is roughly one day a week, assessed over twelve months. A cross-border worker who works from home one day a week is therefore permanently flirting with the limit; at the second day a week, the switch is clear-cut: affiliation in the country of residence, and the Luxembourg employer obliged to register there and pay contributions there. Few employers accept that gladly.
The framework agreement: up to 49.9 % of remote work
Since 1 July 2023, a multilateral framework agreement — signed among others by Belgium, France, Germany and Luxembourg — allows a derogation from the 25 % rule for habitual cross-border telework only: the employee may work from home in their country of residence up to less than 50 % of their working time while remaining affiliated in Luxembourg.
Three conditions shape the arrangement:
- it covers telework from home, not client rounds nor activities in a third country;
- it does not apply automatically: the employer applies to the competent institution of the State whose legislation is sought — to stay affiliated in Luxembourg, the application goes through the Centre commun de la sécurité sociale;
- the agreement takes the form of an A1 document, the proof of affiliation to be produced in the event of an inspection.
Without an application, the 25 % rule takes over again — the framework agreement is an option to be activated, not a right that applies by itself.
Two counters, four situations
Combining the two rules creates situations that look contradictory and are simply parallel:
- One day of remote work per week: below 25 %, but around 47 days in the year — the 34-day tax tolerance is exceeded. Compliant socially, taxed partly in the country of residence.
- 34 days spread over the year: compliant for tax, around 15 % of working time — compliant socially too.
- Two days of remote work per week under the framework agreement: compliant socially, far beyond the 34 tax days.
Neither count excuses you from the other. That is the point of a daily register: the same calendar serves both, provided it exists.