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 July and the most expensive month to fly is January. (Average prices, based on 507 datapoints.)
The best day to arrive at Istanbul is Tuesday and it would be best to avoid Monday, as prices are on average 94.98% higher than on Tuesday. (Average prices, based on 507 datapoints.)