Cheap flights from Seattle to London (SEA to LHR) from $1,468

The cheapest month to fly is January, and departing on Thursdays typically offers the best fares. Book 6–8 weeks ahead for the best prices.

Book at the right time: For international flights, aim to book 6–10 weeks ahead. Last-minute fares on Seattle to London are rarely cheap, and prices spike sharply within 2 weeks of departure.

Shift your dates by a day or two: Thursdays are typically the cheapest day to fly this route. Avoiding Friday and Sunday departures can save significantly. January is historically the cheapest month on this route.

Weigh up connecting flights: Connecting flights on Seattle to London can be 20–40% cheaper than direct options. If you have time to spare, it's worth comparing.

Factor in baggage fees: Low-cost carriers on this route often advertise attractive base fares but charge separately for checked luggage. Always compare the all-in price — a $20 cheaper fare plus $50 baggage fee is no saving. United Airlines and Air Canada may have different inclusions, so check each airline's fare conditions.

Search in private browsing: Some booking sites use cookies to track repeat searches and may show higher prices after multiple lookups. Use an incognito or private window — or just use Booked AI, which pulls live prices without any tracking markup.

Compare two one-ways against a return: On some international routes, booking a one-way with one airline and the return with another can undercut a standard return ticket — especially if a budget carrier covers one direction. Check both options with the flexible dates calendar above.

The cheapest flights from Seattle to London start from $1,468, with typical prices ranging from $1,468 to $1,768.

The typical flight time from Seattle to London is approximately 15 hours and 42 minutes.

Airlines operating this route include United Airlines, Air Canada, WestJet, Icelandair, Aer Lingus, Virgin Atlantic, Lufthansa, Turkish Airlines, British Airways, China Airlines, Austrian, American Airlines, Finnair, Aeromexico, Alaska Airlines, Brussels Airlines, SAS.