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

Return flights

06 Dec - 12 Dec	Icelandair
31 Dec - 14 Jan	British Airways
09 Dec - 13 Jan	British Airways
09 Dec - 27 Jan	British Airways
08 Dec - 20 Jan	British Airways
08 Dec - 13 Jan	British Airways
07 Dec - 30 Jan	British Airways
08 Dec - 15 Dec	Lufthansa
06 Dec - 14 Dec	British Airways
09 Dec - 23 Dec	Delta
07 Dec - 15 Dec	Delta
22 Dec - 17 Jan	KLM
06 Dec - 11 Dec	KLM
04 Dec - 12 Dec	KLM
31 Dec - 14 Jan	Turkish Airlines	direct
04 Dec - 23 Dec	Delta
28 Dec - 11 Jan	Air France
15 Dec - 15 Jan	KLM
06 Dec - 20 Dec	Alaska Airlines
08 Dec - 15 Dec	Turkish Airlines	direct

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

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 December from 473€

Return flights