Please be aware that Brussels has multiple airports and that these results are for all airports serving the city.
The best month to fly between Brussels and Madrid is May and the most expensive month to fly is March. (Average prices, based on 305 datapoints.)
The best day to arrive at Brussels is Thursday and it would be best to avoid Sunday, as prices are on average 111.51% higher than on Thursday. (Average prices, based on 216 datapoints.)
The cheapest airline flying from Brussels to Madrid is Ryanair. They are 34% cheaper than Air Europa. (Average prices, based on 309 datapoints.)