Upon departure or a few days earlier, you have to deregister yourself as a resident of Belgium.
Exception: if you have applied for Bijlage 33, you do not have to deregister. Reason being that your main address is abroad
Procedure:
Deregistration is done directly with the Antwerp immigration desk online through Welkom | Antwerpen.be. The webpage is in Dutch.
You will immediately be on the page ‘Afschrijving naar het buitenland voor niet-Belgen aanvragen’ (deregistration application for non-Belgians). Go down the page until you see ‘Vul het formulier in’ (Fill out the form - in blue colour). Select it. You will notice that there are several options to log on - with itsme, with eID and card reader, with security code through mobile app or with federal token. If you choose one of these options, you will need to download the eID software or the itsme app for this to work. All your data will then be picked from the National Register and filled out automatically. You can also choose the option ‘verdergaan zonder aanmelden’ (continue without using the above options). Then you will have to complete all the requested data manually.(in Dutch).
Complete the electronic form and submit it.
After processing, a document called Model 8, proof of deregistration (in Dutch) will be sent to your email address.
Important
Do not forget to deregister, otherwise you will continue to be a Belgian resident according to the Belgian authorities. Failure to deregister could have important consequences for visa requirements, taxes, health insurance registration and so on if you return to Belgium in the future.