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

Return flights

29 Aug - 03 Sep	United
02 Aug - 09 Aug	Spirit Airlines
03 Aug - 09 Aug	Spirit Airlines
07 Aug - 13 Aug	Spirit Airlines
30 Aug - 06 Sep	Delta
02 Aug - 04 Aug	Spirit Airlines
18 Aug - 25 Aug	Alaska Airlines
16 Aug - 23 Aug	Alaska Airlines
03 Aug - 04 Aug	Spirit Airlines
01 Aug - 15 Aug	Alaska Airlines
02 Aug - 10 Aug	Spirit Airlines
01 Aug - 09 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 393€

Return flights