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

Return flights

17 Sep - 24 Sep	Icelandair	direct
27 Sep - 04 Oct	Icelandair	direct
21 Sep - 26 Sep	Icelandair	direct
21 Sep - 25 Sep	Icelandair	direct
17 Sep - 21 Sep	Icelandair	direct
27 Sep - 11 Oct	Icelandair	direct
17 Sep - 11 Oct	Icelandair	direct
21 Sep - 11 Oct	Icelandair	direct
20 Sep - 11 Oct	Icelandair	direct
26 Sep - 05 Oct	Icelandair	direct
18 Sep - 24 Sep	United
19 Sep - 21 Sep	United
23 Sep - 20 Oct	Icelandair	direct
17 Sep - 27 Sep	Icelandair	direct
20 Sep - 27 Sep	Icelandair	direct
19 Sep - 21 Sep	Icelandair	direct
26 Sep - 29 Sep	SWISS
30 Sep - 08 Oct	British Airways

Also check the deals for one-way flights from Washington to Keflavik 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 Washington to Keflavik in September from 314€

Return flights