Two obligations, often confused
Declaration of works or Checkinatwork?
This is the question most contractors call about. The declaration of works — also called site notification or “30bis” — and Checkinatwork are two separate obligations with the same authority, the NSSO (RSZ/ONSS). They have different thresholds, a different rhythm and a different person responsible. Doing one does not put you in order for the other.
Declaration of works
You report the site, once, before the start.
Checkinatwork
You report the people, every working day.
Side by side
What do you report?
- Declaration of works
- The site: which works, where, by whom, when.
- Checkinatwork
- Who is actually present on the site that day.
How often?
- Declaration of works
- Once, before the start (and updated when things change).
- Checkinatwork
- Every working day, for every person present.
Who does it?
- Declaration of works
- The declarant: the contractor engaged by the client.
- Checkinatwork
- Every employer for their own people; self-employed workers for themselves.
From what amount?
- Declaration of works
- From €30,000, or from €5,000 with at least one subcontractor.
- Checkinatwork
- From €500,000 total site value (works on immovable property).
What do you get?
- Declaration of works
- A site number.
- Checkinatwork
- A receipt number per registration as proof.
When do you need to submit a declaration of works?
The declaration obligation (article 30bis) applies to works on immovable property and to the delivery of ready-mixed concrete. The rule of thumb:
- From €30,000 excl. VAT per client–contractor contract, with or without subcontractors.
- From as little as €5,000 excl. VAT as soon as you bring in at least one subcontractor.
- For works involving asbestos: always, regardless of the amount.
- For temporary or mobile construction sites and asbestos removal: at least 15 calendar days before the start.
The declaration is made by the contractor engaged by the client. Only that declarant can create or amend the declaration — the other parties in the chain can only view it. As a subcontractor, you therefore pass on your own subcontractors to the declarant.
Why you need the site number
This is where the two obligations meet: the declaration of works produces a site number, and that number is exactly what you use to register attendance in Checkinatwork. Sites covered by attendance registration are identified through that number from the declaration. No declaration therefore means no site to check in on.
Note: the reverse doesn't hold. Submitting a declaration of works does not mean you also have to register attendance — for that, the site has to be above the €500,000 threshold. Many sites must be declared but are not subject to attendance registration.
The order in practice
1. Declaration of works
The main contractor declares the site to the NSSO before the start. Result: a site number.
2. Letter from the NSSO
If the site is above the threshold, the NSSO notifies the declarant that attendance must be registered. They pass this on to all parties on the site.
3. Attendance registration
From then on, every employer registers their people daily on that site number through Checkinatwork.
4. From 2027
Registration happens in real time on site, in and out, by the worker themselves.
You submit the declaration of works yourself with the NSSO — AutoCheckIn plays no part in that. What we take over is steps 3 and 4: the daily registration. Here's how to sign up on the NSSO portal.
Frequently asked questions
What is the difference between the declaration of works and Checkinatwork?
The declaration of works (also called site notification or 30bis) registers the site itself with the NSSO: who is carrying out the contract, where and when. You do it once, before the start. Checkinatwork records who is actually present on that site on a given day, and you do that again every working day. So the declaration does not replace attendance registration.
When do I have to submit a declaration of works?
Rule of thumb: for every contract between client and contractor of €30,000 or more excl. VAT, with or without subcontractors, and from as little as €5,000 excl. VAT as soon as you bring in at least one subcontractor. For works involving asbestos, the declaration is mandatory regardless of the amount. Check your specific situation with your social secretariat.
Who has to submit the declaration of works?
The contractor engaged by the client — in other words, the main contractor. Only that declarant can create or amend the declaration; the other parties in the chain can only view it. Subcontractors must, however, pass on their own subcontractors to the declarant.
How far in advance must the declaration be made?
Before the works start. For a temporary or mobile construction site or asbestos removal, the declaration must be made at least 15 calendar days before the start.
What is the site number for?
The declaration of works produces a site number. That number identifies the site, and it is exactly the number you need to register attendance in Checkinatwork. No declaration, no site number, no registration.
I've made a declaration of works — do I also have to register attendance?
Only if the site is above the attendance registration threshold (€500,000 excl. VAT for works on immovable property). The declarant receives a letter from the NSSO about this. The two thresholds are therefore different: many sites must be declared but are not subject to attendance registration.
Does anything change in 2027?
The declaration of works stays as it is. What changes is attendance registration: check-in and check-out, in real time on site, by the worker themselves, from 1 April 2027.
Read more
- What is Checkinatwork (CIAW)?
- Registering for Checkinatwork with the NSSO
- When is Checkinatwork mandatory?
- Adding a subcontractor to Checkinatwork
This page is general information, not legal advice. The thresholds and deadlines for the declaration of works are published by the NSSO on socialsecurity.be; check your specific situation with your social secretariat or accountant.