Please be aware that Frankfurt has multiple airports and that these results are for all airports serving the city.
The best month to fly between Frankfurt and Amsterdam is June and the most expensive month to fly is August. (Average prices, based on 247 datapoints.)
The best day to arrive at Frankfurt is Wednesday and it would be best to avoid Thursday, as prices are on average 137.83% higher than on Wednesday. (Average prices, based on 303 datapoints.)
The best time to fly is at around 19. (Average prices, based on 418 datapoints.)