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

Return flights

21 Aug - 28 Aug	Frontier Airlines
23 Aug - 30 Aug	Frontier Airlines
22 Aug - 24 Aug	Frontier Airlines
31 Aug - 06 Sep	Frontier Airlines
30 Aug - 06 Sep	Frontier Airlines
28 Aug - 05 Sep	Frontier Airlines
31 Aug - 04 Sep	Frontier Airlines
18 Aug - 23 Aug	Frontier Airlines
29 Aug - 04 Sep	Frontier Airlines
20 Aug - 25 Aug	Frontier Airlines
29 Aug - 01 Sep	Frontier Airlines
23 Aug - 30 Aug	United	direct
30 Aug - 06 Sep	United	direct

Also check the deals for one-way flights from Denver 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 Denver to San Juan in August from $268

Return flights