$104 Cheap United flights Harlingen (HRL) to St. Louis (STL)

You can discover affordable return United Airlines flights from $260 from HRL to STL by filtering your results from "Price (lowest to highest)" on Expedia. Or search for bargains from $104 for a one-way journey.**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.

To find cheap United Airlines fares from Valley Intl. Airport (HRL) to Lambert-St. Louis Intl. Airport (STL), start searching one to three months before your planned departure. Securing domestic flights 34 to 86 days in advance could save you 25% compared to booking just 6 to 12 days ahead. The day you book can also affect how much you pay. Sunday tends to be the cheapest, while Monday is often the most expensive for domestic flights. You can save 6% on average by booking on a Sunday.**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.

Find United Airlines's earliest flights from HRL to STL by selecting our "Morning" and "Early Morning" filters. Not only will you get to your destination sooner, early departures also have a 20% less chance of being canceled.**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.

Offering a rewarding loyalty program, United Airlines is a favorite of many passengers journeying from HRL to STL. Plus, as a United Mileage Plus and One Key™ member booking through Expedia, you can earn OneKeyCash™* on eligible flights along with your airline miles.*OneKeyCash™ disclaimer - OneKeyCash™ is not redeemable for cash and can only be used on Expedia, Hotels.com and Vrbo.