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

Return flights

02 Sep - 11 Sep	TAP
17 Sep - 01 Oct	Turkish Airlines
01 Sep - 10 Sep	SWISS
02 Sep - 09 Sep	United
14 Sep - 28 Sep	SWISS
11 Sep - 18 Sep	United
05 Sep - 12 Sep	United
08 Sep - 15 Sep	United
14 Sep - 21 Sep	United
24 Sep - 01 Oct	United
29 Sep - 06 Oct	United
19 Sep - 26 Sep	United

Also check the deals for one-way flights from Washington to Sofia 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 Sofia in September from $624

Return flights