AirHint found the following cheapest return flights from Ontario (ONT) to San Francisco (SFO) in December 2025 (see full year).

Return flights

09 Dec - 11 Dec	Frontier Airlines
11 Dec - 16 Dec	Frontier Airlines
15 Dec - 15 Dec	Frontier Airlines
26 Dec - 16 Jan	United	direct
17 Dec - 02 Jan	Frontier Airlines
18 Dec - 02 Jan	Frontier Airlines
01 Dec - 17 Dec	Frontier Airlines
11 Dec - 16 Jan	Southwest Airlines
29 Dec - 05 Jan	Frontier Airlines	direct
20 Dec - 08 Jan	Southwest Airlines
31 Dec - 03 Jan	Southwest Airlines
28 Dec - 31 Dec	Southwest Airlines
22 Dec - 03 Jan	Southwest Airlines
29 Dec - 03 Jan	Southwest Airlines
20 Dec - 23 Dec	Alaska Airlines

Also check the deals for one-way flights from Ontario to San Francisco 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 Ontario to San Francisco in December from $171

Return flights