Washington (IAD) to Seattle (SEA): On-Time Performance
Data through July 2026
The calendar drives reliability on IAD–SEA. November 2024 flights landed on schedule 95% of the time, but December 2025 dropped to 48% — a gap of 47 points. Across the full period the route averages 80% on-time against a national 78%. Morning departures also hold up better than evening ones (85% vs 71%), which matters most in the rough months.
- On-time
- 80%
- arrived <15 min late
- Avg delay
- 14 min
- completed flights
- Cancelled
- 0.9%
- Flights/day
- 5.1
- last 12 months
- Duration
- 5h 52m
- scheduled
- Distance
- 2,305 mi
Best airline from IAD to SEA
3 airlines flew this route regularly between 2024-07 and 2026-07.
| Airline | On-time | Avg delay | Cancelled | Flights |
|---|---|---|---|---|
| United Airlinesmost reliable | 82% | 13 min | 0.8% | 1,623 |
| Delta Air Lines | 81% | 19 min | 0.8% | 896 |
| Alaska Airlines | 77% | 13 min | 1.0% | 1,770 |
Monthly on-time trend
Best time to fly from IAD to SEA
Aim for departures around 11 a.m. (96% on-time); avoid 6 p.m. departures (63%).
By day of week
| Day | On-time | Avg delay |
|---|---|---|
| Monday | 79% | 13 min |
| Tuesday | 81% | 13 min |
| Wednesdaybest | 81% | 13 min |
| Thursday | 80% | 18 min |
| Friday | 80% | 13 min |
| Saturday | 79% | 14 min |
| Sunday | 79% | 15 min |
What causes delays on this route
Share of total delay minutes by cause, as reported by carriers to the US DOT.
- Late-arriving aircraft25%
- Airline operations37%
- National airspace system26%
- Weather12%
- Security1%
Frequently asked questions
- How often are flights from IAD to SEA delayed?
- 20% of IAD–SEA flights arrived 15 or more minutes late (the US DOT definition of a delay) between 2024-07 and 2026-07. The average arrival delay across completed flights was 14 minutes.
- Which airline is most reliable from IAD to SEA?
- United Airlines has the best on-time record on this route at 82%, based on 1,623 flights. 3 airlines flew IAD–SEA frequently enough to compare in this period.
- What is the best time of day to fly from IAD to SEA?
- Departures around 11 a.m. have the best record (96% on-time), while departures around 6 p.m. have the worst (63%). As on most US routes, delays accumulate through the day, so earlier flights are generally safer.
- How long is the flight from IAD to SEA?
- The scheduled IAD–SEA flight time averages 5h 52m over 2,305 miles. Actual arrival times vary — flights on this route land 15+ minutes late 20% of the time.
- How often are IAD to SEA flights cancelled?
- 0.9% of scheduled flights on this route were cancelled between 2024-07 and 2026-07, at or below the national rate of 1.6%.
- What is the worst month to fly from IAD to SEA?
- December 2025 was the roughest month in this dataset, with only 48% of arrivals on time. The best was November 2024 at 95%. If your dates are flexible, that 47-point gap is worth planning around.
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Based on 4,289 flights, 2024-07–2026-07. Source: US DOT Bureau of Transportation Statistics. Updated 2026-09-28.