DimDay is the same-day version of the Dimona declaration, and every flexi-job shift needs one. Before a flexi-job worker starts, you must file a Dimona naming that worker for that day, and it has to be filed before work begins. There is no grace period and it cannot be done after the fact. If a worker starts a shift without a valid DimDay on file, Belgian social security law treats that day as regular employment, which means full employer contributions and the loss of the worker’s tax advantage for that day. Suivo’s check-in at work solution links each scheduled shift to DimDay support and flags a missing declaration before work starts, so you never discover the gap during an audit. For the full flexi-job picture, see our complete employer guide.
What is a DimDay, and how is it different from a normal Dimona?
Dimona is Belgium’s immediate employment declaration to the NSSO, the record that a given worker is employed by a given employer. For most workers it is filed once when employment starts.
DimDay is the flexi-job form of that declaration. Because a flexi-job is worked shift by shift, the declaration has to happen shift by shift too. Each DimDay states which worker is coming in on a specific day. So where a permanent hire generates one Dimona at the start of the contract, a flexi-job worker who does ten shifts in a month generates ten DimDay declarations, one before each shift.
The declaration is what makes the day count as a flexi-job. Without it, there is no legal basis for the reduced social charge treatment on that day.
When exactly must the DimDay be filed?
The timing rule is strict and there is no flexibility in it.
- Before the shift starts. The DimDay must be on file before the worker begins work, not during the shift and not at the end of it.
- Same day. It is a same-day declaration tied to the specific date the worker attends.
- No grace period. There is no allowance for filing shortly after the worker starts. Late is the same as missing.
- No retroactive filing. You cannot declare a shift after it has happened to fix a gap. A day worked without a prior DimDay stays a day worked without a DimDay.
This is why DimDay is an operational discipline, not a paperwork task. The declaration has to fit into the moment a worker is confirmed for a shift, which for flexi-jobs is often hours or minutes before they arrive.
What happens if a shift runs without a valid DimDay?
This is the expensive scenario. If a flexi-job worker starts without a valid DimDay, that day loses its flexi-job status and is treated as regular employment:
- Full employer social security contributions apply to that day’s wages, instead of the flexi-job arrangement.
- The worker’s tax advantage is lost for that day.
- Repeated gaps compound. Across multiple workers or multiple days, the retroactive NSSO assessment can become significant, and it is assessed after the fact when you can no longer correct it.
The mistake is usually not deliberate. It is a busy shift lead who put a worker to work before the declaration went in, or a last-minute replacement nobody declared. That is exactly why the safeguard has to be systematic. We cover the consequences in detail in what happens with no valid Dimona.
How does SIOD check DimDay during an inspection?
SIOD social inspectors check DimDay timestamps during sector audits, particularly in horeca, retail, care, and events where flexi-jobs are common. Their check is straightforward and hard to argue with: they compare the DimDay filing time against when the worker actually worked.
That comparison is only possible because both facts are timestamped. The DimDay carries the filing time. The working hours, since 1 July 2026, must come from an electronic time registration system. If the time record shows a worker on site before the DimDay was filed, or shows a worker with no DimDay at all, the inspector has a clear finding. This is why the same-day declaration and electronic time registration are two halves of one obligation, explained further in flexi-jobs now require electronic time registration.
How does Suivo support DimDay without slowing the shift down?
The DimDay itself is filed to the NSSO, so it is not a Suivo product feature. What Suivo does is make sure the declaration and the shift stay linked, so gaps surface before work begins rather than during an audit.
- Scheduled shifts drive the check. Because scheduling knows which flexi-job workers are rostered for the day, the platform knows which DimDay declarations should exist.
- A missing declaration is flagged early. When a scheduled flexi-job worker does not yet have a same-day Dimona on file, the platform can flag it, so you file before the worker starts.
- Check-in captures the proof. Presence registration records the verified time the worker actually arrived, giving you the timestamp that must line up with the DimDay if an inspector asks.
The thesis holds here: real-time data has to lead to a decision. A flag that a DimDay is missing is only useful because it prompts you to file before the worker clocks in, which is the one moment that matters. See how flexi-jobs fit a mixed shift in managing a mixed workforce.
Ready to close the DimDay gap before your next shift?
Suivo links scheduled flexi-job shifts to DimDay support and captures verified check-in times, so declarations and hours always line up when SIOD checks.
