A Dimona aangifte (Dimona declaration) is the electronic notice you send to the RSZ (National Social Security Office) when someone starts or stops working for you. You file the Dimona IN at the latest when the worker actually starts, and the Dimona OUT by the first working day after the contract ends. Without it, you break the Social Penal Code and face a fine per worker. Foreign workers posted to Belgium under their home social security usually need Limosa instead.
Dimona says who is employed. Your time registration shows who actually works, where and for how long. Suivo’s time tracking for field teams keeps that second record for crews on sites and on the road.
What is a Dimona declaration?
Dimona stands for déclaration immédiate / onmiddellijke aangifte (immediate declaration of employment). According to the RSZ instructions, all public and private employers must report every hiring and every departure electronically.
Every declaration feeds your personeelsbestand (staff register), which you can consult online. The DmfA, your quarterly social security return, must use the same employer number as your Dimona.
Who must file a Dimona, and who does not?
Who is declared. According to the RSZ scope rules, Dimona covers everyone reported in the DmfA: manual and office workers, apprentices, statutory staff, students, occasional workers and more. It also covers some people outside Belgian social security, such as workers a Belgian employer sends abroad who no longer fall under the Belgian system.
Who is not declared. No Dimona is needed for:
- volunteers;
- self-employed people working in your company;
- PWA/ALE workers and certain household staff;
- workers posted to Belgium by a foreign company who stay under a foreign social security system under an international agreement. As a rule, these posted workers need a Limosa declaration instead.
Foreign employers. Belgian social security applies to work done in Belgium for an employer established in Belgium. It also applies when a foreign employer has an operating seat in Belgium that the worker depends on, unless a treaty says otherwise. The Limosa FAQ sets out the practical cases:
| Situation | Limosa | Dimona and DmfA |
|---|---|---|
| Foreign employer, worker works only in Belgium for an indefinite period | No | Yes |
| Foreign employer, worker in Belgium for a fixed period, posting conditions met (A1) | Yes | No |
| Foreign employer, fixed period, posting conditions not met | Yes | Yes |
| Belgian employer, worker usually works abroad and stays under foreign social security | Yes | Dimona without DmfA (worker type DWD) |
When must you file it?
- Dimona IN: at the latest when the worker actually starts work. You may file earlier. The start date you enter is the start of the contract, which can be earlier than the first working day. Example from the RSZ: contract from 1 May, first working day 5 May. File by 5 May, with start date 1 May.
- Dimona OUT: at the latest on the first working day after the contract ends. Not needed if you already gave the end date in the Dimona IN.
- Fixed end dates: for students, temporary agency workers, occasional workers, IBO/PFI/FPI trainees and certain apprentices, you give the end date with the IN, so no OUT follows.
- Not a departure: a suspension of the contract (including a long posting abroad) or a move between full-time and part-time work.
Occasional workers in agriculture and horticulture are declared per day, with start and end time. For flexi-jobs, see our article on the cost of a missing flexi-job Dimona.
How to file a Dimona step by step
Step 1: identify yourself as an employer. You need a definitive or provisional RSZ number or a company number. If you have none, identify through the WIDE service, reachable from Dimona. You get an RSZ number immediately after the procedure.
Step 2: get the worker’s INSZ. The INSZ (NISS in French) is the national register number for residents, or a BIS number for people without one. If the worker does not know it, request it through belgianIDpro, the secured Sigedis service. You need a good scan of an ID card, passport or driving licence and the worker’s basic identity data. For occasional workers (except in hospitality), the INSZ is mandatory: a temporary foreign worker without a valid BIS number cannot be declared.
Step 3: choose your channel. Dimona is electronic only. SMS is not accepted.
| Channel | Best for |
|---|---|
| Web, unsecured | Filing before you are registered on the portal, or without identifying yourself |
| Staff register (secured), including Multi-Dimona | Regular employers, several workers at once |
| Batch (file transfer) | High volumes from a payroll system |
| Web service (REST) | Software-to-software integration |
| Dimona Mobile | Filing from a mobile device |
| Social secretariat or service provider | Employers who outsource payroll |
You can mandate an approved social secretariat, but you remain responsible for every declaration.
Step 4: enter the data. Give the worker’s INSZ, the joint committee, the worker type and the start date (plus the end date where required).
Step 5: check the notification. You receive a positive, negative or provisional notification. You have 5 working days to dispute its data. After that, the data is final.
If Dimona is down: you must still declare. Report the problem with the RSZ emergency form, report when it is solved, then file normally.
Dimona IN, OUT, UPDATE and CANCEL: which one when?
| Declaration | Use it when | Deadline |
|---|---|---|
| IN | A worker starts | At the latest when work actually starts |
| OUT | A worker leaves and no end date was given | First working day after the end |
| UPDATE (earlier start) | The real start date is earlier than declared | By the real start of work |
| UPDATE (end date) | The real end date is earlier or later | Under the OUT rules |
| CANCEL | The worker does not show up | End of the day concerned; for 2 days or more, end of the first planned day |
Three rules prevent most errors:
- A later start date cannot be updated. Cancel the period and create a new one.
- A cancel removes the whole period, including the IN, OUT and any UPDATE.
- A changed characteristic (joint committee, worker type, sub-entity) needs an OUT plus a new IN. A wrong characteristic needs a cancel and a new declaration.
Worker types and codes you will meet
The RSZ code list includes:
| Code | Worker type |
|---|---|
| BCW | Construction manual worker |
| RTA | Construction apprentice |
| STU | Student with a student contract |
| FLX | Flexi-job |
| EXT | Occasional worker (PC 144, 145, 302, 320, 322) |
| ALT | Dual-learning apprentice |
| IVT | IBO/PFI/FPI trainee |
| DWD | Dimona without DmfA (foreign-insured worker) |
| OTH | All others |
Construction tip: a manual construction worker is BCW, not OTH, and you must give joint committee 124. Construction workers placed by a temp agency use PC 322.
Joint committees. You give the number explicitly for 124, 140, 144, 145, 149 (subcommittee 149.01), 302, 320 and 322. All other joint committees are reported as “XXX”.
Students on a student contract who work at the reduced solidarity contribution must be declared as STU, at the latest on the day they start. A late STU Dimona loses the reduced contribution for all hours in it.
What does a missing or late Dimona cost?
Not filing a Dimona on time, or cancelling too late, is a level 4 offence under the Social Penal Code. According to the FOD WASO (Federal Public Service Employment), for offences committed from 1 February 2026 (the same effective amounts apply from 1 September 2026):
- administrative fine: EUR 3,000 to EUR 35,000 per worker;
- criminal fine: EUR 6,000 to EUR 70,000 per worker, and/or prison of 6 months to 3 years.
The fine is multiplied by the number of workers, up to 100 times.
On top of the fine:
- Solidarity contribution. When an inspector finds a missing Dimona, you owe the RSZ a flat contribution per worker. For 2026 the minimum is EUR 3,674.09. Contributions you actually declared for that worker are deducted.
- Loss of reductions. Since 1 July 2026, for intentional Dimona offences, a court can also withdraw your RSZ contribution reductions for the workers and quarters concerned.
How Dimona, Limosa and Checkinatwork differ
| Dimona | Limosa | Checkinatwork | |
|---|---|---|---|
| Question it answers | Is this person employed under Belgian social security? | Who is coming to work temporarily in Belgium from abroad? | Who is on this site today? |
| Who files | The employer | The foreign employer (or the self-employed person in risk sectors) | Employers and contractors, or the worker |
| When | At the latest when work starts | Before work starts | Every day, before work starts |
| Scope | All employees | Workers and certain self-employed people under foreign social security | Construction sites of EUR 500,000 or more, ready-mix delivery, meat |
One worker can need more than one. A posted construction worker needs Limosa and, on a site of EUR 500,000 or more, a daily attendance registration. From 1 April 2027, according to the RSZ, construction and ready-mix attendance moves from Check in at Work to Check in and out at work. For the full comparison, read Limosa, Dimona and Checkinatwork: the difference.
Linking Dimona to your time registration
A Dimona proves a contract exists. It does not prove who came to work. The risk sits in the gap: a new hire who starts on site before HR has filed, or a worker who left but still clocks in.
A simple daily routine closes that gap:
1. Start from registered presence. Every person who checks in (by app, badge, site pole or vehicle) should appear in your staff register with an open Dimona period.
2. Flag the mismatches. Someone registered on site without an open period needs a Dimona IN before work starts, not at the end of the month.
3. Close the loop at departure. When a contract ends early, file the UPDATE or OUT and deactivate the worker’s badge or app access on the same day.
Suivo gives you the presence record for step 1. Field workers register hours via the mobile app, a badge, a fixed check-in pole on site or automatically through their vehicle. Every registration lands in one validation dashboard. Approved hours sync to your planning, ERP and payroll systems through Suivo’s open API. Suivo can also export hours to your social secretariat: ask us about your provider. For the payroll side, see how to export time registration to payroll and our guide to time registration and your social secretariat.
Frequently asked questions
What is the Dimona declaration?
Dimona (déclaration immédiate / onmiddellijke aangifte) is the electronic declaration every Belgian employer files with the RSZ when a worker starts or leaves. It tells the RSZ that someone works for you and feeds your online staff register.
How can I view my Dimona declarations?
Log in to the secured staff register (personeelsbestand) on the social security portal. It shows every Dimona period you declared. After each declaration you also receive a notification, and you have 5 working days to dispute its data.
How can I cancel a Dimona?
Use a Dimona CANCEL if the worker does not show up. You can cancel until the end of the calendar day concerned, or for a period of 2 days or more, until the end of the first planned day. A cancel removes the whole period.
What is the relation between Dimona and the staff register?
Every Dimona IN, OUT, UPDATE and CANCEL is recorded in the personeelsbestand (staff register). The staff register is also a channel to file Dimona, including several workers at once with Multi-Dimona.
Does a foreign employer have to file a Dimona?
It depends. A worker posted temporarily under foreign social security generally needs a Limosa declaration instead. A foreign employer whose worker works only in Belgium for an indefinite period files a Dimona and a DmfA, not Limosa.
See who is really working today
Dimona tells the RSZ who you employ. Your time registration tells you who is actually on site. When both records match, you avoid the fines and your payroll runs on real hours. See how Suivo connects field registrations to your back office.
