AirHint found the following cheapest return flights from Washington (DCA) to Lisbon (LIS) in September 2025 (see full year).

Return flights

04 Sep - 11 Sep	Air Canada
10 Sep - 17 Sep	Air Canada
09 Sep - 16 Sep	Air Canada
07 Sep - 14 Sep	Air Canada
14 Sep - 21 Sep	Air Canada
28 Sep - 05 Oct	jetBlue
20 Sep - 27 Sep	jetBlue
03 Sep - 10 Sep	Air Canada
08 Sep - 15 Sep	jetBlue
06 Sep - 13 Sep	Scandinavian Airlines
21 Sep - 29 Sep	Air Canada
26 Sep - 02 Oct	United
30 Sep - 08 Oct	United
25 Sep - 01 Oct	United
26 Sep - 04 Oct	Delta
26 Sep - 01 Oct	United
17 Sep - 01 Oct	Air Canada
21 Sep - 01 Oct	British Airways
18 Sep - 03 Oct	British Airways

Also check the deals for one-way flights from Washington to Lisbon 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 Lisbon in September from 437€

Return flights