Declaring employees in Belgium

To enable a correct follow-up by the Belgian social security, an employer must submit two types of declaration for his employees.

You are required to declare every new person you take on and every person leaving your employment to the NSSO. It is important that you submit this declaration correctly and on time: before an employee starts working for you, a Dimona must be in place for them.

Dimona is used for any type of employment contract.

Dimona declarations are filed digitally, in the secure online service Dimona. To be able to use the service, you must be registered on the Belgian social security portal.

What do you need to declare?

You will need to fill in the following basic information in Dimona:

  1. the employee’s national registration number or, if this is not available, their identification details,
  2. additional information about the employee: Joint Committee and employee type,
  3. the period for which the employee will work: start date and end date (if known). For occasional staff: likewise the start and end date.

Explanations of terms such as Joint Committee (Paritair Comité) and the types of employees can be found on the page 'Données principales à renseigner' (What information should I provide?) under 'Instructions administratives ONSS' (Administrative instructions of the NSSO) (in French).

As an employer, you must declare the work done by and salaries paid to your employees every quarter in the multifunctional declaration DmfA. The information from the DmfA is sent to various Belgian social security institutions.

DmfA declarations are filed digitally in the secure online service  DmfA (in French). To be able to use the service, you must be registered on the Belgian social security portal (in French).

What is the DmfA for?

The DmfA’s main functions are:

  • to determine the amount of social security contributions employers and employees need to pay
  • to submit to the government in a one-off communication the salary and work information of all employees

The Belgian social security system applies to:

  • employees who work on Belgian territory and whose employer is based in Belgium
  • employees who are attached to the Belgian registered office of a foreign company

These employees have to be declared in Dimona and DmfA, just as Belgian employees are.

The only exceptions are residents of countries with which Belgium has concluded an international treaty or a bilateral agreement stipulating that the Belgian system does not apply. A list of these countries can be found on the page Coming2Belgium Agreements.

The Dimona and, in particular, the DmfA are closely linked to Belgian employment and social security legislation. Given the critical importance of filling them in correctly, the social security institutions provide comprehensive legal information. This information is regularly updated. It can be found on the Belgian social security portal under the heading 'Instructions administratives ONSS’ (in French) (Administrative instructions of the NSSO).

The declarations are outsourced by many employers to a social secretariat (accredited by the Minister of Social Affairs) or a payroll services firm. An accredited social secretariat is empowered to collect your social security contributions, while a payroll services firm is not.

To mandate a third party to submit declarations for you, use the secure online service 'Mahis' (in French) on the Belgian social security portal.