What is Dimona? Declaration, deadlines and fines (2026) | Peepel
Gert-Jan Vermote · 9 min · 2026-08-10
Dimona is the mandatory Belgian social security declaration you must file before a new employee's first working day. Filing late costs at least EUR 3,674.09 per employee in 2026.
Key takeaways
- Dimona is the electronic declaration of an employee's start and end of employment to the Belgian social security office (NSSO/RSZ). Every Belgian employer must file it.
- Start of employment: before the first working day. End of employment: at the latest the first working day after.
- A missing declaration triggers a solidarity contribution of three times the basic contributions on the guaranteed average minimum monthly income, with a 2026 minimum of EUR 3,674.09 per employee.
- Dimona is not DmfA: Dimona reports the moment, DmfA reports wages and working time each quarter.
- Peepel assembles the declaration from data you already have and sends it to your payroll agency (sociaal secretariaat), which files it with the NSSO.
What is a Dimona declaration?
Dimona (Déclaration Immédiate / Onmiddellijke Aangifte) is the electronic messaging system every employer in Belgium, public or private sector, uses to report an employee's start or end of employment to the NSSO (National Social Security Office, RSZ/ONSS). That is also how the social security office describes it in its guidance on Dimona and the personnel register (consulted 2026). Without a valid Dimona declaration an employee is formally not registered, regardless of what your contract or HR system says.
Key takeaway: Dimona is not an HR formality on the side. It is the legal step that turns a hire into a registered employment.
When must you file Dimona?
- Start of employment: before the employee actually starts working, not afterwards.
- End of employment: at the latest the first working day after the effective end of employment.
Those deadlines are set out in the administrative instructions DmfA 2026/2 on Dimona obligations, together with the rules for modifying and cancelling a declaration.
That "before the first working day" is where things usually go wrong in practice: a contract gets signed, the start date shifts, or the declaration gets stuck between HR and the payroll agency, and it arrives too late.
What does a late or missing Dimona declaration cost?
Belgian social security foresees three types of sanctions for a late or missing Dimona declaration:
- A solidarity contribution: it amounts to three times the basic contributions on the guaranteed average minimum monthly income, with a statutory minimum indexed to the health index. For 2026 that minimum is EUR 3,674.09 per employee, per the NSSO instructions on the solidarity contribution for failing to file a Dimona declaration. Note the word minimum: this is a floor, not a fixed rate. The amount is reduced by the contributions already due for the actual work performed, and can be adjusted pro rata for part-time work if you can prove that full-time work was materially impossible.
- Administrative fines, on top of the solidarity contribution.
- Criminal sanctions for repeated or manifest breaches.
Key takeaway: a missed Dimona declaration is not an accounting footnote. It is a sanction that runs into the thousands of euros per employee.
Dimona vs. DmfA: not the same thing, but connected
Dimona and DmfA are often confused, yet they cover a different moment:
|
Dimona |
DmfA |
| What |
Immediate notification of start and end of employment |
Quarterly declaration of wages and working time |
| When |
Before the first working day (or the first working day after the end) |
Per quarter, after the work is performed |
| Why |
Formally opens and closes the employment |
Reports what happened inside that employment |
Dimona formally opens the employment; DmfA reports afterwards what happened inside it. Your payroll agency handles both, but the data has to arrive correctly and on time for them to file it, which is exactly where HR systems matter. More on that data flow in automating payroll.
How Peepel approaches it
Classic HR software (level 2-3: system of record / system of workflow) records the hiring data and then leaves an HR colleague to retype or forward it to the payroll agency. Peepel works at level 4: system of execution: on the contract or employee form you switch the Dimona option on, and Peepel assembles the declaration from the data that already exists and sends it to your payroll agency. The agency files it with the NSSO, and Peepel then tracks the NSSO verdict, so you can see whether the declaration was accepted. You retype nothing, and you don't have to log into a second system to check whether it worked.
Two things we phrase deliberately. First: this is not a hidden button. For white-collar and blue-collar staff you indicate yourself whether a Dimona has to go out, and day students, for instance, are declared day by day. Second: Peepel does not file with the NSSO itself. That stays with your payroll agency.
Which payroll agencies is this live for? Today for a subset of Belgian payroll agencies. If you work with another one, that does not mean no Dimona happens. It means it is filed on your agency's side rather than sent by Peepel. Just ask us whether yours is included.
Coming from our own payroll-tech background, we saw how many error-prone, manual steps usually sit between a signed contract and a correct Dimona declaration: every retyping step is a chance for a late or incorrect declaration. Letting the declaration start from data that already exists removes exactly those steps. What that looks like for a full hire is covered in automating onboarding.
What level is your HR at?
One simple test: when a new employee starts, does someone have to retype data into a second system and then check there whether the declaration was accepted? If so, you're at level 2 or 3 (organising). If the declaration starts from the data you already have and the result comes back without you looking anywhere else, you're at level 4 (executing).
If you're looking for a platform that works at that fourth level, the best HRIS software in Belgium 2026 compares the options for the Belgian market.
Want to see how this works in practice?
Book a demo and see how a hire in Peepel leads to a sent Dimona request, with no step in between.
Further reading: Automate onboarding · Automate payroll · Best HRIS software Belgium 2026 · Digitise HR processes
FAQ
- Who has to file a Dimona declaration?
- Every employer in the public or private sector in Belgium, for every employee starting or leaving, with no sector exceptions.
- What happens if I forget a Dimona declaration?
- The NSSO can impose a solidarity contribution of three times the basic contributions on the guaranteed average minimum monthly income, with a 2026 minimum of EUR 3,674.09 per employee. That minimum follows the health index and is therefore adjusted annually. Administrative fines and criminal sanctions are possible on top of it.
- When must a Dimona declaration be filed?
- A start of employment must be declared before the employee actually starts working. An end of employment must be declared at the latest the first working day after the effective end date.
- Is Dimona the same as DmfA?
- No. Dimona reports immediately when someone starts or stops; DmfA reports wages and working time within that employment on a quarterly basis.
- Does Peepel file the Dimona declaration itself?
- Peepel assembles the declaration and sends it to your payroll agency when you switch the Dimona option on in the contract or employee form; the agency then files it with the NSSO, and Peepel tracks the NSSO verdict. That is live today for a subset of Belgian payroll agencies. If you work with another one, the Dimona happens on their side.
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