$90 Cheap United flights St. Louis (STL) to Seattle (SEA)

Finding cheap one-way United Airlines flights from STL to SEA from $90 on Expedia couldn't be easier --- just filter by "Price (lowest to highest)." Alternatively, check out our budget-friendly return fares from $180 for your next exciting getaway.**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 ahead of your departure date to score cheap fares on United Airlines flights from Lambert-St. Louis Intl. Airport (STL) to Seattle - Tacoma Intl. Airport (SEA). You can save 25% by booking your domestic flight 34 to 86 days in advance compared to last-minute reservations made 6 to 12 days out. You could also reduce costs by buying your fare on a Sunday, as it's 6% cheaper on average than a Monday, the most expensive day to book.* Get your timing spot on, 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 departures from STL to SEA with United Airlines, filter your results by "Morning" and "Early Morning." Choosing an early flight generally means cancellations are less likely.**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.

A rewarding loyalty program and the ability to collect points through United Mileage Plus are the start of the reasons to fly from STL to SEA with United Airlines. Plus, when you sign up to our One Key™ program, you can earn OneKeyCash™* alongside United Airlines's loyalty program earnings. It's yours to spend on your next adventure.*OneKeyCash™ disclaimer - OneKeyCash™ is not redeemable for cash and can only be used on Expedia, Hotels.com and Vrbo.