Best Time to Fly SEA to IAD: On-Time Stats by Hour & Airline
Seattle/Tacoma International → Washington Dulles International
Data through July 2026 · Last updated October 18, 2026
Over the last 12 months, 83.4% of Seattle (SEA) to Washington (IAD) flights arrived on time (1,853 scheduled flights). That is 5.8 points above the national average of 77.6%.
Among 3 airlines, United Airlines led with 89.1% on time and Delta Air Lines was last with 76.1%.
Over 24 months, Wednesday was the most reliable day (86% on time) and July the worst month (75%).
The cancellation rate was 0.7% (US average 1.8%).
SEA to IAD 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 | 89.1% | 83 min | 0.8% | 657 |
| Alaska Airlines | 82.2% | 38 min | 0.4% | 835 |
| Delta Air Lines | 76.1% | 76 min | 1.1% | 361 |
80%+ good 70–79.9% fair <70% poor
Best time of day to fly SEA to IAD
On-time arrival % by scheduled departure hour (local time), 4,013 flights over 24 months.
Show the numbers
| Departure hour | On time | Cancelled | Flights |
|---|---|---|---|
| 7am–8am | 86.6% | 0.0% | 134 |
| 8am–9am | 89.7% | 0.4% | 911 |
| 9am–10am | 79.2% | 0.0% | 410 |
| 10am–11am | 79.4% | 0.5% | 220 |
| 11am–12pm | Limited data | 9 | |
| 12pm–1pm | 89.8% | 0.9% | 218 |
| 1pm–2pm | 86.3% | 0.5% | 185 |
| 3pm–4pm | 72.3% | 1.5% | 271 |
| 4pm–5pm | 78.5% | 0.2% | 426 |
| 9pm–10pm | 76.8% | 0.3% | 382 |
| 10pm–11pm | 79.5% | 1.0% | 407 |
| 11pm–12am | 79.9% | 1.6% | 440 |
Best day of the week
24 months, by day of departure.
Best month to fly
24 months, by calendar month.
Holiday travel on SEA to IAD
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) | 80.0% | -4.3 pts | 0.0% | 65 |
| Christmas & New Year (Dec 20 - Jan 3) | 90.1% | +5.8 pts | 0.0% | 142 |
| Summer peak (Jun 15 - Aug 15) | 74.5% | -9.8 pts | 0.6% | 946 |
| All other days | 84.3% | — | 0.7% | 2,860 |
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).