If your application for international protection is rejected, you will receive an order to leave the Belgian territory (BGV/OQT).

When do I need to leave Belgium?
The order to leave the Belgian territory will specify a certain period of time during which you may leave Belgium on a voluntary basis. The municipality will invite you for two appointments in view of your return to your country of origin. Please note that by not responding to the municipality’s invites, you may be considered as at risk of absconding – therefor possibly risking detention.

What if I do/can not leave Belgium within the indicated period?
After the expiry of the imposed timeframe for leaving Belgium, the Immigration Office may detain you in a closed detention centre and have you forcibly deported from the territory.
However, in exceptional circumstances (e.g. illness, during the process of organizing a voluntary return,…) the imposed period in which to leave the territory may be extended.