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

Return flights

09 Sep - 23 Sep	Icelandair
23 Sep - 30 Sep	Finnair
03 Sep - 10 Sep	Finnair
16 Sep - 23 Sep	Finnair
17 Sep - 24 Sep	Finnair
24 Sep - 01 Oct	Finnair
25 Sep - 02 Oct	Finnair
26 Sep - 03 Oct	Finnair
30 Sep - 07 Oct	Finnair
22 Sep - 29 Sep	Finnair
20 Sep - 27 Sep	Finnair
09 Sep - 16 Sep	Finnair
10 Sep - 17 Sep	Finnair
21 Sep - 28 Sep	Finnair
27 Sep - 04 Oct	Finnair
28 Sep - 05 Oct	Alaska Airlines
29 Sep - 06 Oct	Finnair

Also check the deals for one-way flights from Seattle to Helsinki 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 Seattle to Helsinki in September from 448€

Return flights