Seattle (SEA) to Denver (DEN): 1,022 miles (1,645 km) great-circle, about 2h 35m nonstop by our estimate. Cheapest fare observed: $242 round-trip on Frontier, nonstop, departing May 10, 2026.
$242 round-trip, Frontier F91176, departing 2026-05-10 at 19:50, returning 2026-05-17. The recorded itinerary left on a Sunday, returning on a Sunday 7 nights later; the fare was observed 15 days before departure. "Book this flight" opens Kiwi.com with the same airline and dates.
At $242, it ranked 8th of the 30 round-trip fares we recorded from SEA (median $591). That is 23.7 cents per great-circle mile (round-trip price over one-way distance), above the SEA median of 19.2 cents across 30 round-trip routes.
Routes from SEA of similar length: San Diego (1,051 mi) at $355 and Ontario, California (957 mi) at $86.
Frontier had the cheapest fare on 10 of 30 SEA routes. It is the 26th longest of the 30 routes we track from SEA.
Of 19 departure airports with a fare to Denver, Seattle (SEA) ranked 14th at $242. Lowest: $49 from Phoenix (PHX); highest: $382 from Guadalajara (GDL); 10 nonstop. Cheapest-fare airlines (routes): Frontier (18) and Viva Aerobus (1).
The reverse, Denver (DEN) to Seattle (SEA), was $178 round-trip on Frontier, nonstop, departing June 22, 2026. Denver to Seattle flights.
Travelpayouts fares (cheapest per route, observed April 25, 2026); OurAirports coordinates and elevations; IANA zones America/Los_Angeles, America/Denver; flight time is our estimate.