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

Return flights

30 Sep - 15 Oct	Delta
29 Sep - 17 Oct	Delta
22 Sep - 01 Oct	Iberia
27 Sep - 08 Oct	KLM
27 Sep - 08 Oct	Aer Lingus	direct
29 Sep - 13 Oct	Aer Lingus	direct
25 Sep - 09 Oct	Aer Lingus	direct
21 Sep - 02 Oct	Aer Lingus
22 Sep - 01 Oct	Aer Lingus	direct
21 Sep - 02 Oct	Aer Lingus	direct
16 Sep - 24 Sep	United
19 Sep - 26 Sep	Aer Lingus	direct
26 Sep - 29 Sep	Frontier Airlines
24 Sep - 27 Sep	Frontier Airlines
25 Sep - 27 Sep	Frontier Airlines
24 Sep - 27 Sep	Aer Lingus	direct
25 Sep - 27 Sep	Iberia	direct

Also check the deals for one-way flights from Denver to Dublin 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 Dublin in September from 424€

Return flights