Seattle, WA

What the Data Says About SEA

Seattle, WA in Seattle, Washington handled 1,871,155 flights in the Bureau of Transportation Statistics dataset between 2020 and 2025, posting a 83.1% on-time departure rate. Of those flights, 315,819 experienced delays, 13,720 were cancelled, and 2,147 were diverted. The cancellation rate works out to 0.73%, the diversion rate to 0.11%, and the average delay when departures run late is 63.4 minutes. These figures are the baseline for comparing SEA against other airports in the same state and nationally.

Breaking down what drives delays at SEA, Carrier leads the pack. Carrier accounts for 44.3% of total delay minutes, followed by Late Aircraft at 28.6% and NAS (National Aviation System) at 21.0%. Weather contributes 5.8% of delay minutes at this airport, while security holds the smallest share at 0.3%. Travelers often overestimate the weather share; the BTS categorization shows late-arriving aircraft and carrier operations as the larger contributors.

Seasonally, October runs the cleanest at SEA with a 93.3% on-time rate, while December is the roughest at 89% — a 4-point swing between best and worst month. Volume peaks in August, when average flights hit 30,041. The busiest route from SEA is to LAX (Los Angeles), with 41,859 flights at a 84% on-time rate. Combine these numbers — 83.1% on-time, 63.4-minute average delay, 0.73% cancellation rate — and you have a concrete picture of departure reliability at Seattle, WA.