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

Return flights

30 Sep - 14 Oct	Finnair	direct
23 Sep - 30 Sep	TAP
17 Sep - 30 Sep	SWISS
16 Sep - 24 Sep	TAP
03 Sep - 10 Sep	Finnair	direct
16 Sep - 24 Sep	Finnair	direct
03 Sep - 12 Sep	Finnair	direct
03 Sep - 12 Sep	TAP
20 Sep - 30 Sep	TAP
04 Sep - 08 Sep	TAP
16 Sep - 23 Sep	Finnair	direct
04 Sep - 22 Oct	TAP
29 Sep - 13 Oct	TAP
26 Sep - 03 Oct	TAP
29 Sep - 06 Oct	TAP
26 Sep - 03 Oct	Iberia	direct
29 Sep - 13 Oct	United	direct
04 Sep - 22 Oct	Finnair	direct

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 300€

Return flights