Cheapest return flights from Seattle to Keflavik in September from $589

Best time to book flights for Seattle (SEA) to Keflavik (KEF) flights at AirHint

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

Return flights

23 Sep - 03 Oct Alaska Airlines
29 Sep - 07 Oct Alaska Airlines
23 Sep - 01 Oct Alaska Airlines
27 Sep - 07 Oct jetBlue
27 Sep - 08 Oct jetBlue
22 Sep - 03 Oct jetBlue
22 Sep - 30 Sep jetBlue
03 Sep - 11 Sep jetBlue
09 Sep - 17 Sep jetBlue
15 Sep - 23 Sep jetBlue
23 Sep - 02 Oct Alaska Airlines
30 Sep - 08 Oct Alaska Airlines
22 Sep - 01 Oct jetBlue
04 Sep - 11 Sep jetBlue
23 Sep - 29 Sep Alaska Airlines
09 Sep - 20 Sep Alaska Airlines
13 Sep - 23 Sep jetBlue
13 Sep - 22 Sep jetBlue
12 Sep - 23 Sep jetBlue
17 Sep - 02 Oct jetBlue

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

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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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