Washington to Seattle

What the Data Says About IAD to SEA

The Washington to Seattle corridor (IAD → SEA) covers roughly 2,306 miles and is served by 9 carriers, based on Bureau of Transportation Statistics reporting. Across 10,097 flights in the dataset, this route posts a 82% on-time rate with an average delay of 73.4 minutes when flights run late. Over the most recent 24 months of BTS data, 4,197 flights were recorded on this pairing — 49 cancelled (1.2%) and 12 diverted (0.3%). Those baseline metrics tell you what to expect before you book.

Having 9 carriers on the route matters: more carriers generally means more daily schedule options, competitive pricing, and redundancy when flights are cancelled. With 10,097 total flights analyzed, the 82% on-time figure is statistically meaningful rather than a small-sample fluke. The 73.4-minute average delay applies only to flights that actually ran late, so it is not the average wait across all departures — the majority of flights on this route depart on time under the BTS definition of a delay (15+ minutes past schedule).

Looking at recent months, Nov 2024 posted the best performance on this corridor at 96% on-time, while Dec 2025 came in at 49% on-time — a 46-point gap between best and worst recent month. For travelers evaluating the IAD to SEA route, the combination of a 82% on-time rate, 73.4-minute average delay, 1.2% recent cancellation rate, and 9 available carriers is the concrete summary of what BTS data shows about reliability on this pairing.