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 Izmir is May and the most expensive month to fly is June. (Average prices, based on 243 datapoints.)
The best day to arrive at Istanbul is Wednesday and it would be best to avoid Monday, as prices are on average 171.91% higher than on Wednesday. (Average prices, based on 948 datapoints.)
The best time to fly is at around 19. (Average prices, based on 384 datapoints.)