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

Return flights

16 Sep - 15 Oct	Aer Lingus
03 Sep - 09 Sep	Aer Lingus
02 Sep - 11 Sep	Aer Lingus
01 Sep - 17 Sep	Aer Lingus
01 Sep - 16 Sep	Aer Lingus
07 Sep - 14 Sep	Aer Lingus
02 Sep - 16 Sep	Icelandair
15 Sep - 22 Sep	Aer Lingus
02 Sep - 15 Sep	Aer Lingus
14 Sep - 30 Sep	Aer Lingus
02 Sep - 12 Sep	Aer Lingus
16 Sep - 15 Oct	Air France	direct

Also check the deals for one-way flights from Seattle to Amsterdam 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 Amsterdam in September from $524

Return flights