IAD to SEA flight delays
Washington, VA (IAD) Seattle, WA (SEA) · 2,305 miles
1,884 flights · January 2025 – August 2026 · US Bureau of Transportation Statistics
76.57%
Arrived on time
Within 15 minutes of schedule
1.01%
Cancelled
Share of scheduled flights
63 min
When late, late by
Average across delayed arrivals
16 min
Delay per flight
Averaged over every flight flown
What the record says about this route
The season swings this route hard. In September it ran 43.8 points more punctual than in December — a difference bigger than the one between the best and worst airlines on most routes. If the date is flexible, it is worth more than the carrier.
Which airline you fly changes the odds here. United Airlines arrived on time 6 points more often than Alaska Airlines over the same period on the same route — same airports, same weather, same air traffic control. A gap that survives all of that is about how the two airlines are run.
The two directions do not behave alike. SEA to IAD arrives on time 5.4 points more often than the outbound. Delay accumulates through the flying day, so whichever direction is scheduled later tends to carry the worse record — which is an argument for booking the morning departure if the choice exists.
The Washington to Seattle route sits close to the middle of the record — neither notably punctual nor notably late.
Which airline should you fly on this route?
Over January 2025 – August 2026, United Airlines arrived on time most often on IAD to SEA. Alaska Airlines was late most often. Flights ran closest to schedule in September and worst in December.
Every airline on IAD to SEA
Ranked by how many flights each one operated. A carrier with fewer than 100 flights in the period is listed but not graded.
| Airline | Flights | On time | Cancelled | Avg delay | Grade |
|---|---|---|---|---|---|
| Alaska Airlines | 835 | 73.7% | 1.2% | 53 min | D |
| United Airlines | 688 | 79.74% | 0.58% | 61 min | C |
| Delta Air Lines | 361 | 77.18% | 1.39% | 93 min | C |
Month by month
Share of flights that arrived within 15 minutes of schedule, by month flown.
The return leg
SEA to IAD Seattle back to Washington 81.94% on time BOther routes from Washington
Common questions
Are flights from Washington to Seattle usually delayed?
76.57% of flights on the IAD to SEA route arrived within 15 minutes of schedule, so roughly 2 in every ten arrived late. That is about the same as the average route in this record.
Which airline is most on time from Washington to Seattle?
United Airlines, at 79.74% on time across 688 flights. The least punctual on the route was Alaska Airlines at 73.7%.
How often are IAD to SEA flights cancelled?
1.01% of scheduled flights did not operate — about 10 in every thousand. That is in the normal range.
What is the best month to fly Washington to Seattle?
September, when 92.2% of flights arrived on time. The worst was December at 48.4%.
When IAD to SEA flights are late, how late are they?
About 63 minutes on average across the flights that arrived more than 15 minutes behind schedule.
What these figures do and do not tell you
Everything on this page is counted from the flights that actually operated on IAD to SEA during January 2025 – August 2026, as reported by the airlines to the US Bureau of Transportation Statistics. "On time" is the federal definition: arriving at the gate within 15 minutes of the scheduled time.
A route's record is a description of the past, not a forecast. Weather, air traffic control and the aircraft's earlier flights that day drive most delays, and none of them are predictable from a historical rate. What the record does tell you is whether this route runs late more often than others, and which carrier on it has the better history — which is the part you can actually act on when you book.
Cancellations are counted separately from delays because they are a different problem for a traveller: a late flight still gets you there. How the grade is calculated →