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

Return flights

07 Sep - 04 Oct	Singapore Airlines	direct
26 Sep - 16 Oct	Singapore Airlines	direct
20 Sep - 10 Oct	Singapore Airlines	direct
05 Sep - 22 Sep	Air Canada
13 Sep - 28 Sep	Singapore Airlines
24 Sep - 14 Oct	Delta

Also check the deals for one-way flights from Seattle to Singapore 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 Singapore in September from $581

Return flights