AirHint found the following cheapest return flights from Seattle (SEA) to Istanbul (IST) in September 2025 (see full year).

Return flights

29 Sep - 03 Oct	Icelandair
09 Sep - 23 Sep	Icelandair
30 Sep - 13 Oct	Hawaiian Airlines
27 Sep - 11 Oct	Hawaiian Airlines
11 Sep - 23 Sep	Icelandair
26 Sep - 18 Oct	Hawaiian Airlines
07 Sep - 27 Sep	Icelandair
28 Sep - 18 Oct	KLM
16 Sep - 26 Sep	Icelandair
30 Sep - 25 Oct	Hawaiian Airlines
23 Sep - 28 Sep	Hawaiian Airlines
19 Sep - 22 Sep	Hawaiian Airlines
15 Sep - 20 Sep	WestJet
16 Sep - 03 Oct	Frontier Airlines
16 Sep - 13 Oct	Icelandair
11 Sep - 18 Sep	Alaska Airlines
10 Sep - 04 Oct	KLM
12 Sep - 04 Oct	Frontier Airlines
11 Sep - 14 Sep	Alaska Airlines
18 Sep - 28 Sep	Frontier Airlines

Also check the deals for one-way flights from Seattle to Istanbul in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from Seattle to Istanbul in September from 655€

Return flights