$90 Cheap United flights Seattle (SEA) to Ontario (ONT)

Set the "Price (lowest to highest)" filter on Expedia to find cheap United Airlines round-trip flights from $138 from SEA to ONT. Affordable one-way tickets from $90 are also available.**These prices were available on Expedia within the past 7 days, for flights departing within the next year. Prices and availability are subject to change. Additional terms apply.

Begin your search one to three months before your departure to find cheaper fares on United Airlines flights from Seattle - Tacoma Intl. Airport (SEA) to Los Angeles - Ontario Intl. Airport (ONT). You can save 25% by booking your domestic flight 34 to 86 days in advance versus last-minute reservations made 6 to 12 days out. You could also cut costs by buying your fare on a Sunday, as it's 6% cheaper on average than a Monday, the most expensive day to book.* Time it well, and you can enjoy significant savings on domestic trips.*Ideal booking window recommendation is based on average round-trip ticket prices for January through November for 2024. Best day of the week to book recommendation is based on average round-trip ticket prices for January through October 2024. All data sourced from ARC's global airline sales database.

To find the earliest departure from SEA to ONT with United Airlines, filter your search by "Morning" and "Early Morning." Choosing an early flight usually means you're less likely to experience cancellations.**Most reliable time of the day recommendation is based on January through August 2024 flight status data sourced from OAG's global flight data platform.

Fly from SEA to ONT with United Airlines and you can look forward to a range of perks starting with a rewarding loyalty program. When booking through Expedia as a United Mileage Plus and One Key™ member, you could also earn OneKeyCash™* to spend on select future travel purchases.*OneKeyCash™ disclaimer - OneKeyCash™ is not redeemable for cash and can only be used on Expedia, Hotels.com and Vrbo.