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

Return flights

14 Aug - 21 Aug	Air Canada
14 Aug - 22 Aug	Air Canada
14 Aug - 23 Aug	Air Canada
15 Aug - 26 Aug	Air Canada
05 Aug - 12 Aug	Air Canada
31 Aug - 08 Sep	United
23 Aug - 30 Aug	Air Canada
27 Aug - 03 Sep	Air Canada
15 Aug - 25 Aug	Air Canada
04 Aug - 11 Aug	Air Canada
14 Aug - 17 Aug	Air Canada
13 Aug - 24 Sep	Air Canada
05 Aug - 12 Aug	Icelandair	direct
26 Aug - 02 Sep	United
22 Aug - 01 Sep	Lufthansa
28 Aug - 04 Sep	Icelandair	direct
31 Aug - 08 Sep	Icelandair	direct
26 Aug - 02 Sep	Icelandair	direct
27 Aug - 03 Sep	Icelandair	direct
30 Aug - 06 Sep	Icelandair	direct

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

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 Keflavik in August from $477

Return flights