Cheap flights from Seattle to Los Angeles from $109

In general, October is the cheapest month to fly from Seattle to Ontario. Due to it being the ‘off-season’ during this time, you can expect flight prices to be around $187. If you aren’t able to travel during the month of October, then book flights to Ontario from Seattle during September instead. Flights to Ontario in September, while not as cheap as those in October, still average around $206.

The cheapest day to depart on your flight to Ontario is on a Wednesday when prices can be found for as low as $227. This is often the case because there is less demand to fly during this day of the week. When flying out on a Sunday, the most expensive travel day of the week, you can expect to see flight prices from Seattle to Ontario for around $307.

At noon is the cheapest time of day to fly from Seattle to Ontario when you can find flight prices for as low as $201. Flying to Ontario at noon is an ideal time because this is during off-peak travel hours. If you have a flexible travel schedule, then try to avoid flying in the morning when prices are $273 on average. Flights to Ontario from Seattle in the morning are generally more expensive because this time of day is more convenient for travelers’ schedules.

Fly from Seattle/Tacoma Intl to Ontario for the best Seattle/Tacoma Intl - Ontario flight prices

You are more likely to see cheaper flights to Ontario from Seattle when booking weeks ahead of your departure date. In general, you can expect to find flights to Ontario for around $260 when searching weeks out. However, flight prices might be lower outside of this timeframe. For example, people recently found flights to Ontario from Seattle for as low as $192 on momondo.

Southwest, Frontier, and Alaska Airlines are the most popular carriers operating from Seattle/Tacoma Intl to Ontario

Alaska Airlines, Frontier and Delta are the top three most popular airlines that fly to Ontario from Seattle according to our data. Alaska Airlines is the first choice among our users, with 47% of people opting to fly with this airline when traveling to Ontario. Keep in mind that there are 9 different airlines that fly to Ontario on a routine basis, so you have a few additional options to choose from.

Denver (DEN) was the most common stop: 67% of momondo users choosing 1-stop flights on this route connected there.

Flights via Denver (DEN) offer the lowest average round-trip price of $210.

Flights connecting via San Francisco (SFO) have the shortest average one-way travel time: 5h 08m.

San Francisco (SFO) has the shortest average layover time for this route: 1h 03m.

As of April 2026, 12 flights take off from Seattle and land in Ontario each day. The most common flight departure time for this route is 7:00PM, with 36% of daily flights taking off in the evening.

The number of flights available between Seattle and Ontario is 90 per week as of April 2026. The most frequent departure day is Mon, with 17% of weekly flights leaving on this day.