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

Return flights

30 Sep - 07 Oct	Icelandair
02 Sep - 09 Sep	Icelandair
23 Sep - 30 Sep	Icelandair
08 Sep - 15 Sep	Icelandair
02 Sep - 09 Sep	Lufthansa	direct
29 Sep - 06 Oct	Icelandair
30 Sep - 07 Oct	United	direct
17 Sep - 24 Sep	United
11 Sep - 18 Sep	Icelandair
05 Sep - 12 Sep	United	direct
11 Sep - 18 Sep	Lufthansa	direct
08 Sep - 15 Sep	Lufthansa	direct
14 Sep - 21 Sep	United
26 Sep - 03 Oct	United	direct
29 Sep - 06 Oct	United	direct
26 Sep - 04 Oct	United

Also check the deals for one-way flights from Denver to Frankfurt 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 Frankfurt in September from 517€

Return flights