AirHint found the following cheapest return flights from Philadelphia (PHL) to Sofia (SOF) in December 2025 (see full year).

Return flights

09 Dec - 16 Dec	Lufthansa
09 Dec - 23 Dec	Lufthansa
31 Dec - 21 Jan	Frontier Airlines
15 Dec - 10 Jan	Frontier Airlines
30 Dec - 20 Jan	Lufthansa
09 Dec - 18 Dec	Lufthansa
15 Dec - 22 Dec	Aer Lingus
16 Dec - 08 Jan	Frontier Airlines
09 Dec - 21 Dec	Austrian Airlines
21 Dec - 10 Jan	Frontier Airlines
24 Dec - 07 Jan	Spirit Airlines
16 Dec - 22 Dec	Aer Lingus
12 Dec - 01 Jan	Frontier Airlines
16 Dec - 23 Dec	Aer Lingus
23 Dec - 06 Jan	Spirit Airlines
17 Dec - 24 Dec	Spirit Airlines
17 Dec - 28 Dec	Spirit Airlines
09 Dec - 05 Jan	Lufthansa
17 Dec - 23 Dec	Spirit Airlines
09 Dec - 03 Jan	Frontier Airlines

Also check the deals for one-way flights from Philadelphia to Sofia in December.

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 Philadelphia to Sofia in December from 392€

Return flights