Best Time to Fly IAD to SEA: On-Time Stats by Hour & Airline
Washington Dulles International → Seattle/Tacoma International
Data through July 2026 · Last updated October 18, 2026
1,851 flights were scheduled from Washington (IAD) to Seattle (SEA) in the last 12 months, and 77.7% of those that flew arrived on time, in line with the US average of 77.6%.
United Airlines was the most punctual of the 3 airlines on the route at 80.9%, while Alaska Airlines trailed at 75.5%.
September has been the best month (90% on time) and Saturday the weakest day of the week (79%).
1.0% of flights were cancelled, versus 1.8% nationally.
IAD to SEA on-time performance by airline
Last 12 months. Airlines with fewer than 30 completed flights are marked “limited data”.
| Airline | On time | Avg delay when late | Cancelled | Flights |
|---|---|---|---|---|
| United Airlines | 80.9% | 61 min | 0.6% | 655 |
| Delta Air Lines | 76.9% | 93 min | 1.4% | 361 |
| Alaska Airlines | 75.5% | 49 min | 1.2% | 835 |
80%+ good 70–79.9% fair <70% poor
Best time of day to fly IAD to SEA
On-time arrival % by scheduled departure hour (local time), 4,011 flights over 24 months.
Show the numbers
| Departure hour | On time | Cancelled | Flights |
|---|---|---|---|
| 6am–7am | 94.0% | 0.5% | 218 |
| 7am–8am | 82.1% | 0.7% | 1,085 |
| 8am–9am | 93.1% | 0.3% | 294 |
| 9am–10am | 82.8% | 1.3% | 377 |
| 10am–11am | Limited data | 23 | |
| 11am–12pm | Limited data | 19 | |
| 12pm–1pm | 93.0% | 0.0% | 86 |
| 1pm–2pm | 90.3% | 0.0% | 206 |
| 3pm–4pm | Limited data | 8 | |
| 4pm–5pm | 80.0% | 1.7% | 118 |
| 5pm–6pm | 76.0% | 0.6% | 834 |
| 6pm–7pm | 63.7% | 1.3% | 473 |
| 7pm–8pm | 68.1% | 1.8% | 166 |
| 10pm–11pm | 68.0% | 1.0% | 104 |
Best day of the week
24 months, by day of departure.
Best month to fly
24 months, by calendar month.
Holiday travel on IAD to SEA
On-time arrivals during holiday periods compared with all other days, last 24 months.
| Period | On time | vs other days | Cancelled | Flights |
|---|---|---|---|---|
| Thanksgiving week (Tue before to Mon after) | 85.9% | +4.4 pts | 1.5% | 65 |
| Christmas & New Year (Dec 20 - Jan 3) | 71.9% | -9.6 pts | 1.4% | 143 |
| Summer peak (Jun 15 - Aug 15) | 75.9% | -5.6 pts | 0.9% | 946 |
| All other days | 81.5% | — | 0.7% | 2,857 |
Monthly on-time trend
On-time arrival % each month, with the 12-month US average for reference.
What causes delays on this route
Share of reported delay minutes, last 12 months (BTS cause categories).