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

Return flights

19 Sep - 02 Oct	Singapore Airlines	direct
09 Sep - 16 Sep	United
05 Sep - 22 Sep	United
16 Sep - 26 Sep	United
13 Sep - 28 Sep	United
30 Sep - 18 Oct	Korean Air
02 Sep - 07 Sep	Korean Air
01 Sep - 06 Sep	United
17 Sep - 30 Sep	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 527€

Return flights