Upon departure or a few days earlier, you have to deregister yourself as a resident of Antwerp.
The Immigration Office prefers online deregistration through www.antwerpen.be. The website is in Dutch however.
Select E-loket. Then type ‘vertrek’. You will be able to select ‘vertrek naar het buitenland niet-Belg. Select ‘verdergaan zonder A-profiel’. Select ‘aanvraag starten’ and complete the electronic form.
Below deregistration procedure is also an option:
After processing, a document Model 8, proof of deregistration (in Dutch) will be sent to your email address. If you send the document on a later date than the date of departure (= ‘from’ date on the application document), the official date of deregistration will be the date of receipt, not the date of departure.
If you need the proof of deregistration immediately, in order to close your bank account for example, it is best to go to the Immigration Office in Deurne in person and deregister on the spot. A passport picture is required. The document Model 8 will be handed to you immediately.
Do not forget to deregister, otherwise you continue to be a Belgian resident according to the Belgian authorities (tax offices, etc.)