Please be aware that Istanbul has multiple airports and that these results are for all airports serving the city.
The best month to fly between Istanbul and Dusseldorf is June and the most expensive month to fly is August. (Average prices, based on 605 datapoints.)
The best day to arrive at Istanbul is Tuesday and it would be best to avoid Monday, as prices are on average 100.42% higher than on Tuesday. (Average prices, based on 493 datapoints.)
The best time to fly is at around 9. (Average prices, based on 1102 datapoints.)