Please be aware that Brussels and Frankfurt has multiple airports and that these results are for all airports serving the city.
The best month to fly between Brussels and Frankfurt is August and the most expensive month to fly is April. (Average prices, based on 232 datapoints.)
The best day to arrive at Brussels is Monday and it would be best to avoid Tuesday, as prices are on average 65.83% higher than on Monday. (Average prices, based on 213 datapoints.)
The cheapest airline flying from Brussels to Frankfurt is Lufthansa. They are 36% cheaper than Lufthansa CityLine. (Average prices, based on 242 datapoints.)
The best time to fly is at around 13. (Average prices, based on 466 datapoints.)