From:- www.trafficfines.eu/english/belgium-speeding.php

In built-up areas, it's € 50 fixed fine up to 10kph over the limit, then an additional € 10 per kph and if you're more than 20 kph over limit, an 8-day ban and court if more than 30 kph over.

Outside built-up areas it's € 50 fixed fine up to 10kph over the limit, then an additional € 5 per kph and if you're more than 30 kph over limit, an 8-day ban and court if more than 40 kph over.