St. Louis (STL) to Seattle (SEA): On-Time Performance
Data through July 2026
St. Louis (STL) to Seattle (SEA) effectively runs on two schedules. In October 2024, 97% of arrivals were on time; in December 2025 that fell to 55% — a 42-point seasonal swing. Across the full period the route averages 79% on-time against a national 78%. Morning departures also hold up better than evening ones (85% vs 61%), which matters most in the rough months.
- On-time
- 79%
- arrived <15 min late
- Avg delay
- 12 min
- completed flights
- Cancelled
- 0.7%
- Flights/day
- 2.4
- last 12 months
- Duration
- 4h 29m
- scheduled
- Distance
- 1,709 mi
Best airline from STL to SEA
2 airlines flew this route regularly between 2024-07 and 2026-07.
| Airline | On-time | Avg delay | Cancelled | Flights |
|---|---|---|---|---|
| Alaska Airlinesmost reliable | 82% | 11 min | 0.9% | 1,645 |
| Southwest Airlines | 59% | 18 min | 0.0% | 236 |
Monthly on-time trend
Best time to fly from STL to SEA
Aim for departures around 6 a.m. (92% on-time); avoid 5 p.m. departures (39%).
By day of week
| Day | On-time | Avg delay |
|---|---|---|
| Monday | 81% | 11 min |
| Tuesdaybest | 82% | 11 min |
| Wednesday | 81% | 10 min |
| Thursday | 78% | 13 min |
| Friday | 78% | 12 min |
| Saturday | 73% | 13 min |
| Sunday | 80% | 12 min |
What causes delays on this route
Share of total delay minutes by cause, as reported by carriers to the US DOT.
- Late-arriving aircraft35%
- Airline operations34%
- National airspace system25%
- Weather6%
Frequently asked questions
- How often are flights from STL to SEA delayed?
- 21% of STL–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 12 minutes.
- Which airline is most reliable from STL to SEA?
- Alaska Airlines has the best on-time record on this route at 82%, based on 1,645 flights. 2 airlines flew STL–SEA frequently enough to compare in this period.
- What is the best time of day to fly from STL to SEA?
- Departures around 6 a.m. have the best record (92% on-time), while departures around 5 p.m. have the worst (39%). As on most US routes, delays accumulate through the day, so earlier flights are generally safer.
- How long is the flight from STL to SEA?
- The scheduled STL–SEA flight time averages 4h 29m over 1,709 miles. Actual arrival times vary — flights on this route land 15+ minutes late 21% of the time.
- How often are STL to SEA flights cancelled?
- 0.7% 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 STL to SEA?
- December 2025 was the roughest month in this dataset, with only 55% of arrivals on time. The best was October 2024 at 97%. If your dates are flexible, that 42-point gap is worth planning around.
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Based on 1,881 flights, 2024-07–2026-07. Source: US DOT Bureau of Transportation Statistics. Updated 2026-09-28.