You live in one country, work at clients' premises in another and prepare your assignments from home. Your clients' nationality or the address on your invoices is not enough to determine your social security coverage. To have the situation assessed properly, the actual work, its locations and its regularity must be described. Let us build this file before declarations become contradictory.
The framework to review
This guide sets out coordination benchmarks for self-employed activity carried out in several States, mainly within the European framework. Temporary activity, regular activity in several countries and a combination with salaried employment require different analyses. The United Kingdom and third countries require verification of the applicable instruments. The social security decision does not, on its own, determine tax residence, VAT, professional authorisations or residence obligations.
Describe the activities and their actual locations
List each activity, its status, the tasks performed and the places where you carry them out. Distinguish assignments at clients' premises, administrative work, preparation and travel. Foreign clients do not always mean work abroad; conversely, a Luxembourg invoice may remunerate activity carried out elsewhere. The documents must reflect the same situation as your actual organisation.
Activity in several countries involves several professional activities; its international analysis requires, in particular, an understanding of their frequency and how they interact. Prepare a representative schedule, the contracts and the known prospects. Report planned changes instead of presenting a temporary distribution as permanent. Verifiable data are more helpful to the competent institution than a general statement simply indicating “international work”.
Distinguish between a temporary assignment and regular activity
A one-off trip for an assignment similar to the usual activity may be subject to a posting assessment, subject to conditions. Repeated activity in several countries follows a different logic. The CCSS examines, in particular, situations involving self-employed persons affiliated in Luxembourg before leaving for another country. Do not turn a regular succession of assignments into a series of postings without having the classification verified.
The file must specify the foreseeable duration, continuity of the usual activity and the means retained to resume it. The conditions for maintaining coverage cannot be reduced to remaining below a maximum duration. Consult the body before departure and keep the information submitted. A request prepared in advance makes it possible to identify missing information without having to urgently reorganise an assignment that has already started.
Review residence and the share of activity
In cases of activity in several countries, the CCSS states that the competent body at the place of residence must be contacted to determine the applicable legislation. For self-employed activities in several States, the analysis examines, in particular, whether a substantial part is carried out in the State of residence; otherwise, the centre of interest of the activities is taken into consideration. This centre cannot be inferred solely from the choice of an administrative address.
The European Commission cites turnover, working time, services provided and income among the useful criteria. The 25 % benchmark is used in an overall assessment of the substantial part. A percentage calculated on a single invoice should therefore not be treated as an automatic decision. Present the available data, their calculation method and their limitations so that the institution can assess the whole situation.
Report any combination with salaried employment
If you also hold salaried employment, report it from the outset, together with the countries where the work is actually carried out. The combination of salaried and self-employed activity does not simply follow the rule for several self-employed activities. The national classification of certain roles, particularly management roles, may also differ. The same title in two contracts does not guarantee identical social security status in both countries.
Gather certificates and decisions already received, without assuming that they cover every new activity. The principle of one applicable legislation within the relevant coordination framework means that the whole situation must be assessed, including income that must be taken into account. The guide to self-employed contributions will be useful once Luxembourg affiliation and the income to be declared have been clarified.
Obtain proof and monitor changes
The A1 certificate certifies the applicable social security legislation in the relevant situations. It does not replace an authorisation to practise or a tax analysis. Check the persons, activities, States and periods covered, then keep a copy accessible during assignments. For countries outside the relevant framework, ask which document and agreement must be used.
Inform the institution of significant changes: moving home, a new country of work, changes to salaried employment or a lasting change in the distribution of activities. Keep reasonable records of work performed to explain these developments. The guide distinguishing tax and social security rules complements this approach, but tax tolerances and salaried teleworking arrangements must not be automatically applied to self-employed activity.
The table for taking action
| Information | Example of evidence | Why it matters |
|---|---|---|
| Residence | Documented personal situation | Institution to contact |
| Nature of activities | Contracts and description of tasks | Self-employed, salaried or combined |
| Locations and frequency | Schedule and assignments | Temporary or regular |
| Weight of activities | Time, income and services | Overall assessment |
| Existing decisions | Certificates and periods | Scope and changes to report |
The client's country is not always the country of work
Fictional example: a consultant residing in Belgium invoices Luxembourg clients. She performs part of the work from home and regularly travels to her clients' premises. She then adds salaried employment. For the social security assessment, she describes the actual locations and status of each activity, then contacts the competent institution in her country of residence. The example does not conclude which country of affiliation applies: it shows why the list of invoices and the business address are not sufficient to decide.
Your preparation checklist
- Describe all activities and their statuses.
- Identify residence and actual locations.
- Separate temporary assignments from regular work.
- Prepare a schedule and economic data.
- Report any salaried employment.
- Contact the competent institution.
- Check the scope and period of the certificate.
- Declare significant changes.
Frequently asked questions
Can I choose the country where contributions are lowest?
The applicable legislation follows the coordination rules and the actual situation, not a free choice of rates.
Does an A1 settle my tax matters?
No. It concerns the applicable social security legislation. Tax obligations must be examined separately.
Is the 25 % threshold calculated solely on sales?
For self-employed activity, several criteria may be used in the overall assessment, including time, turnover, services and income.
Useful terms in this guide
Questions to ask the professional
- Does our description cover all my activities?
- Which institution must determine the legislation?
- Which changes will require a new review?
To clarify the assignment to be entrusted, also consult our payroll and social security administration file.
What about your situation?
Prepare your contracts, a work schedule and the certificates already received. Search our directory for a professional to structure the file and coordinate the assessment with the relevant social security bodies.
Sources and verification
References consulted on 20 September 2026. Official procedures specify the applicable conditions and exceptions.
- CCSS — activité indépendante à l’étranger
- Commission européenne — coordination sociale, activités dans plusieurs États
- CCSS — revenu professionnel de l’indépendant
This guide explains a general process. The applicable rules depend on your situation; it does not constitute personalised advice. Report a correction.
Your next step
A specific need deserves the right contact
Accounting, taxation, company formation or payroll: prepare your questions, then search the directory for the professional who can review your situation. Check their assignments and status before entrusting them with your file.