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

Return flights

21 Sep - 01 Oct	TAP
22 Sep - 01 Oct	TAP
16 Sep - 24 Sep	TAP
26 Sep - 07 Oct	TAP
29 Sep - 07 Oct	TAP
26 Sep - 01 Oct	TAP
30 Sep - 07 Oct	TAP
22 Sep - 03 Oct	United
23 Sep - 03 Oct	United
21 Sep - 01 Oct	Finnair	direct
21 Sep - 02 Oct	Finnair	direct
23 Sep - 30 Sep	United
22 Sep - 30 Sep	Lufthansa
15 Sep - 22 Sep	TAP
07 Sep - 16 Sep	TAP
16 Sep - 18 Sep	TAP
15 Sep - 23 Sep	Air Canada
09 Sep - 16 Sep	United
15 Sep - 23 Sep	Finnair	direct
10 Sep - 25 Sep	Lufthansa

Also check the deals for one-way flights from Washington 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 Washington to Madrid in September from 337€

Return flights