Seattle (SEA) to St. Louis (STL): On-Time Performance
Data through July 2026
The calendar drives reliability on SEA–STL. April 2026 flights landed on schedule 98% of the time, but June 2025 dropped to 53% — a gap of 45 points. Across the full period the route averages 78% on-time against a national 78%.
- On-time
- 78%
- arrived <15 min late
- Avg delay
- 11 min
- completed flights
- Cancelled
- 0.3%
- Flights/day
- 2.4
- last 12 months
- Duration
- 3h 55m
- scheduled
- Distance
- 1,709 mi
Best airline from SEA to STL
2 airlines flew this route regularly between 2024-07 and 2026-07.
| Airline | On-time | Avg delay | Cancelled | Flights |
|---|---|---|---|---|
| Alaska Airlinesmost reliable | 80% | 9 min | 0.2% | 1,644 |
| Southwest Airlines | 60% | 18 min | 0.4% | 236 |
Monthly on-time trend
Best time to fly from SEA to STL
Aim for departures around 5 p.m. (91% on-time); avoid 11 a.m. departures (58%).
By day of week
| Day | On-time | Avg delay |
|---|---|---|
| Monday | 79% | 10 min |
| Tuesday | 80% | 9 min |
| Wednesday | 79% | 9 min |
| Thursday | 75% | 13 min |
| Friday | 77% | 12 min |
| Saturday | 74% | 12 min |
| Sundaybest | 81% | 9 min |
What causes delays on this route
Share of total delay minutes by cause, as reported by carriers to the US DOT.
- Late-arriving aircraft37%
- Airline operations40%
- National airspace system21%
- Weather2%
Frequently asked questions
- How often are flights from SEA to STL delayed?
- 22% of SEA–STL 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 11 minutes.
- Which airline is most reliable from SEA to STL?
- Alaska Airlines has the best on-time record on this route at 80%, based on 1,644 flights. 2 airlines flew SEA–STL frequently enough to compare in this period.
- What is the best time of day to fly from SEA to STL?
- Departures around 5 p.m. have the best record (91% on-time), while departures around 11 a.m. have the worst (58%). As on most US routes, delays accumulate through the day, so earlier flights are generally safer.
- How long is the flight from SEA to STL?
- The scheduled SEA–STL flight time averages 3h 55m over 1,709 miles. Actual arrival times vary — flights on this route land 15+ minutes late 22% of the time.
- How often are SEA to STL flights cancelled?
- 0.3% 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 SEA to STL?
- June 2025 was the roughest month in this dataset, with only 53% of arrivals on time. The best was April 2026 at 98%. If your dates are flexible, that 45-point gap is worth planning around.
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Based on 1,880 flights, 2024-07–2026-07. Source: US DOT Bureau of Transportation Statistics. Updated 2026-09-28.