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

Return flights

27 Sep - 30 Sep	United	direct
21 Sep - 25 Sep	United	direct
28 Sep - 03 Oct	United	direct
28 Sep - 04 Oct	United	direct
26 Sep - 30 Sep	United
14 Sep - 25 Sep	United	direct
16 Sep - 20 Sep	United
17 Sep - 19 Sep	Delta
01 Sep - 30 Sep	United	direct
20 Sep - 22 Sep	Frontier Airlines
14 Sep - 18 Sep	United
20 Sep - 28 Sep	Frontier Airlines
25 Sep - 01 Oct	Frontier Airlines
28 Sep - 05 Oct	Frontier Airlines

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 $276

Return flights