$404 Cheap United flights Washington (IAD) to London (LHR)

✔️ Prices were available within the past 7 days and start at $404 for one-way flights and $592 for roundtrip, for the period specified. Prices and availability are subject to change. Additional terms apply.

✔️ The airfares published on Expedia.com over the past 7 days saw the lowest prices for one-way departures in August and round-trip departures in March.

✔️ Use the interactive calendar available on Expedia to see the cheapest United (Chantilly IAD - London LHR) ticket prices during the weeks surrounding your travel dates. Compare flight prices for similar timeframes and adjust departure and return dates to get the cheapest fare possible. The lowest-priced days are highlighted in green.

While it’s impossible to guarantee when to find the lowest prices, our data currently suggests that March seems to be the cheapest month to take roundtrips and August seems to have the lowest one-way prices. Plane tickets for flight routes with one or more stops can sometimes be cheaper.

✔️ Three weeks out can be the best time to book flights with various airlines on diverse routes according to ARC & Expedia Group historical data. The data also suggests that if book on a Sunday, you could possibly save up to 20% on fares*.

✔️ ARC & Expedia Group historical data suggests that travelers can save on diverse routes when starting their journey on a Thursday for international flights and on a Friday for domestic flights*. The cheapest day of the week to fly changes based on seasonal demand and route popularity. We recommend using the ‘Show flexible dates’ feature at the top of your search.

✔️ Airlines have different policies and fees for changes or cancellations. It’s important to review the ‘rules + restrictions’ section in your itinerary. We recommend filtering for ‘No change fees’ to see flexible plane tickets. Some airlines charge steep fees, while others are more flexible. Basic Economy or Light Fare tickets are generally non-refundable, but most airlines allow free cancellations or changes within 24 hours after booking. Find out more about changing or canceling your flight reservation by navigating to ‘My Trips’ and selecting ‘Change My Flight.’

*Data specialists from both ARC and Expedia Group analyzed ARC’s global flight data to distill actionable information to help people save money on travel. While it’s impossible to guarantee when to find the lowest prices, after examining the variables, we were able to observe trends.Best day of the week to book and travel recommendation is based on average round-trip ticket prices for January through early October, for both 2019 and 2020, sourced from ARC’s global airline sales database.