Cheap flights from Seattle to London (SEA to LHR) from $709

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: Mid-week departures (Tuesday–Wednesday) are almost always cheaper than weekend flights. Even shifting by one day can make a meaningful difference.

Direct flights are available: Direct flights take around 15h 22m and are worth it for convenience — but check if a one-stop flight is significantly cheaper before ruling it out.

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. Aer Lingus 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 $709, with typical prices ranging from $709 to $890.

The typical flight time from Seattle to London is approximately 15 hours and 22 minutes. Direct flights are available on this route.

Airlines operating this route include Aer Lingus, Air Canada, Alaska Airlines, American Airlines, Austrian, British Airways, Brussels Airlines, China Airlines, Finnair, Iberia.