AirHint found the following cheapest return flights from Washington (DCA) to San Juan (SJU) in September 2025 (see full year).

Return flights

20 Sep - 28 Sep	Southwest Airlines
19 Sep - 28 Sep	Southwest Airlines
17 Sep - 20 Sep	Southwest Airlines
19 Sep - 21 Sep	Southwest Airlines
02 Sep - 11 Sep	Southwest Airlines
18 Sep - 23 Sep	Southwest Airlines
17 Sep - 24 Sep	Southwest Airlines
24 Sep - 26 Sep	Delta
18 Sep - 22 Sep	Southwest Airlines
23 Sep - 28 Sep	Southwest Airlines
30 Sep - 05 Oct	United
25 Sep - 02 Oct	United

Also check the deals for one-way flights from Washington to San Juan 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 Washington to San Juan in September from 243€

Return flights