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

Return flights

17 Sep - 24 Sep	Frontier Airlines
06 Sep - 13 Sep	Frontier Airlines
04 Sep - 08 Sep	Frontier Airlines
11 Sep - 15 Sep	Frontier Airlines
25 Sep - 29 Sep	Frontier Airlines
10 Sep - 15 Sep	Frontier Airlines
27 Sep - 11 Oct	United
30 Sep - 14 Oct	United
25 Sep - 29 Sep	United	direct
25 Sep - 09 Oct	United	direct
18 Sep - 02 Oct	United
22 Sep - 06 Oct	United
29 Sep - 13 Oct	United
09 Sep - 23 Sep	United
12 Sep - 26 Sep	United
14 Sep - 28 Sep	United
20 Sep - 04 Oct	United	direct
23 Sep - 07 Oct	United
24 Sep - 08 Oct	United
26 Sep - 10 Oct	United	direct

Also check the deals for one-way flights from Denver 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 Denver to San Juan in September from 187€

Return flights