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

Return flights

05 Sep - 13 Sep	Icelandair	direct
05 Sep - 12 Sep	Icelandair	direct
13 Sep - 18 Sep	Icelandair	direct
17 Sep - 24 Sep	Icelandair	direct
01 Sep - 12 Sep	Icelandair	direct
12 Sep - 20 Sep	Icelandair	direct
13 Sep - 20 Sep	Icelandair	direct
06 Sep - 12 Sep	Icelandair	direct
23 Sep - 30 Sep	Icelandair	direct
18 Sep - 24 Sep	Icelandair	direct
26 Sep - 05 Oct	Icelandair	direct

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.

Book a cheap hotel in Keflavik

Cheap car rent in Keflavik

Cheapest return flights from Washington to Keflavik in September from $311

Return flights