AirHint found the following cheapest return flights from Seattle (SEA) to San Juan (SJU) in August 2025 (see full year).

Return flights

24 Aug - 04 Sep	United
30 Aug - 06 Sep	United
18 Aug - 22 Aug	Alaska Airlines
01 Aug - 15 Aug	United
18 Aug - 25 Aug	Alaska Airlines
22 Aug - 26 Aug	United
23 Aug - 26 Aug	Alaska Airlines
24 Aug - 28 Aug	Southwest Airlines
28 Aug - 03 Sep	Alaska Airlines
28 Aug - 31 Aug	Alaska Airlines

Also check the deals for one-way flights from Seattle to San Juan in August.

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 San Juan in August from 338€

Return flights