AirHint found the following cheapest return flights from Chicago (MDW) to Madrid (MAD) in September 2025 (see full year).

Return flights

23 Sep - 30 Sep	KLM
15 Sep - 23 Sep	Delta
23 Sep - 29 Sep	KLM
10 Sep - 17 Sep	Delta
08 Sep - 04 Oct	Virgin Atlantic
28 Sep - 05 Oct	Delta
26 Sep - 29 Sep	Frontier Airlines
21 Sep - 26 Sep	Frontier Airlines
12 Sep - 14 Sep	Frontier Airlines
19 Sep - 18 Oct	Frontier Airlines
25 Sep - 28 Sep	Frontier Airlines
22 Sep - 29 Sep	Frontier Airlines
19 Sep - 22 Sep	Frontier Airlines
19 Sep - 11 Oct	Frontier Airlines
18 Sep - 05 Oct	Frontier Airlines
30 Sep - 25 Oct	Virgin Atlantic
26 Sep - 04 Oct	Delta
28 Sep - 18 Oct	Air France
27 Sep - 02 Oct	Delta

Also check the deals for one-way flights from Chicago to Madrid 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 Chicago to Madrid in September from 433€

Return flights