Embaucher son premier employé en Belgique : le guide complet

Hiring your first employee is a milestone — and in Belgium, it comes with a significant administrative load. Get it right and it's smooth sailing. Get it wrong and you could face fines, back payments, and labour disputes. Here's the complete roadmap.

Step 1: Register as an Employer with ONSS/RSZ

Before the first working day, you must register as an employer with the National Social Security Office (ONSS/RSZ). This is non-negotiable. You'll need your company number (BCE/KBO) and VAT number ready.

Step 2: File the DIMONA Declaration

The DIMONA (Déclaration Immédiate / Onmiddellijke Aangifte) is an electronic notification filed before the employee's first working day. It declares the start of the employment relationship to the social security system.

• Deadline: Before the first day of work.
• Fines for late filing: €300–€3,000 (administrative) or €600–€6,000 (criminal).
• How: Via the social security portal or through your social secretariat.

This is the single most common mistake made by first-time employers — don't skip it.

Step 3: Draft the Employment Contract

Written contracts are legally required and must be provided within 2 months of employment (immediately for fixed-term/part-time contracts).

Mandatory content: identification of both parties, job description, start date/duration, gross salary and benefits, working hours (standard: 38 hours/week), workplace, notice period terms, and reference to the applicable Joint Committee/CBA.

Critical — the language requirement: The contract must be in the official language of the region: Dutch in Flanders, French in Wallonia, either in Brussels. Using the wrong language can nullify the contract.

Step 4: Understand the Real Cost

An employee's total cost to you is approximately 1.5× the gross salary:

• Employer social contributions: ~25% (white-collar) to ~35% (blue-collar) of gross salary
• Employee social contributions: 13.07% (withheld from salary)
• Withholding tax: Progressive, withheld monthly
• 13th month: One month's salary in December (pro-rated first year)
• Holiday bonus: 92% of monthly gross in June

Example: An employee with a €3,500 gross monthly salary costs approximately €4,375/month in employer contributions alone, plus ~€6,720/year in bonuses. Annual total employer cost: approximately €59,220.

Step 5: Partner with a Social Secretariat

This is the single most valuable recommendation. A social secretariat (secrétariat social/sociaal secretariaat) — such as Acerta, Liantis, SD Worx, or Partena Professional — handles DIMONA, DmfA quarterly declarations, payroll calculation, payslip generation, holiday pay, and compliance. For a first hire, this is practically essential and costs approximately €50–€100/month per employee.

Step 6: Quarterly DmfA Filing

Every quarter, you must file the DmfA (Déclaration multifonctionnelle / Multifunctionele Aangifte) with ONSS, detailing payroll data and working time. Your social secretariat handles this, but you remain responsible for accuracy.

Key Numbers at a Glance

• Minimum wage (GAMMI, 2025): €2,111.89/month (38-hour week)
• Annual leave: 20 days (4 weeks)
• Sick leave: 100% paid by employer first 30 days
• Maternity leave: 15 weeks
• Paternity leave: 20 days
• Cost reduction for first hires: Up to 25% ONSS reduction for SMEs

The bottom line: Budget 1.5× the gross salary, partner with a social secretariat, and triple-check the DIMONA filing. With these three things in place, your first hire will be smooth.