$159 Cheap Frontier Airlines flights St. Louis (STL) to Seattle (SEA)

You can discover budget-friendly return Frontier Airlines flights from $192 from STL to SEA by sorting your results from "Price (lowest to highest)" on Expedia. Or look for bargains from $159 for a one-way trip.**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.

Look for affordable Frontier Airlines flights from Lambert-St. Louis Intl. Airport (STL) to Seattle - Tacoma Intl. Airport (SEA) one to three months ahead of your departure. Travelers who book domestic flights 34 to 86 days in advance can save 25% compared to those who book just 6 to 12 days ahead. Regardless of fare type and journey, the ideal day to book a domestic flight is generally Sunday and the most expensive tends to be Monday. Passengers who book on a Sunday can save 6% on average compared to those who book on a Monday.**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.

Filter your results by "Morning" and "Early Morning" to browse the earliest flights from STL to SEA. Taking off early 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.

With a rewarding loyalty program, Frontier Airlines is a top choice for many passengers heading from STL to SEA. Plus, if you're a Frontier Miles and One Key™ member booking through Expedia, you could earn OneKeyCash™* on eligible flights on top of your airline miles.*OneKeyCash™ disclaimer - OneKeyCash™ is not redeemable for cash and can only be used on Expedia, Hotels.com and Vrbo.