84% of flights from Seattle to St. Louis arrived on time over the past 12 months. That is better than the typical U.S. route. The 7 a.m. departures ran on time 95% of the time; the 6 p.m. ones 81%. Most reliable airline: Alaska Airlines (85%). 3% of flights arrived more than an hour late or not at all.
How late?
The on-time rate treats a flight 20 minutes late the same as one 5 hours late. Here's the split for SEA → STL: when a flight was late, it was under 45 minutes late 68% of the time. About 1 in 37 flights landed an hour or more late, and 1 in 147 three hours or more; 0.3% were cancelled outright.
- On time or early84%
- 15–30 min late7.7%
- 30–60 min late5.1%
- 1–2 hours late1.6%
- 2–3 hours late0.5%
- 3+ hours late0.7%
- Diverted0.2%
- Cancelled0.3%
Share of all 883 scheduled flights, past 12 months, by arrival time against schedule.
By airline
| Airline | Flights | On time | Cancelled | Typical arrival | 1h+ late | Avg when late | Operated by |
|---|---|---|---|---|---|---|---|
| Alaska Airlines | 780 | 85% | 0.3% | −12 min | 2.3% | +48 min | Alaska Airlines |
| Southwest Airlines | 103 | 73% | 1.0% | +2 min | 5.8% | +55 min | Southwest Airlines |
Airline = the name on the ticket. Regional flights (e.g. "Delta Connection") count under the ticketing airline, and the operator is listed.
Best time of day to fly
On-time rate by scheduled departure hour (local time at SEA). Delays build through the day as late planes knock on, so early flights usually do best.
By airline and hour
| Departs | Alaska Airlines |
|---|---|
| 7 a.m. | 95% |
| 9 a.m. | 89% |
| 6 p.m. | 81% |
Last flight of the day
On SEA → STL, each airline's last flight of the day was cancelled 0.3% of the time, against 0.0% for its earlier flights, about the same. It arrived 3+ hours late 0.7% of the time (earlier flights: 0.7%). It matters more than the numbers suggest. Miss an earlier flight and there's another one that evening; miss the last one and you're usually waiting until morning.
| Airline | Last departure | Last: cancelled | Last: 3h+ late | Earlier: cancelled | Next morning |
|---|---|---|---|---|---|
| Alaska Airlines | 6:04 p.m. | 0.3% | 0.7% | 0.0% | first flight 7:55 a.m. |
Last flight = the airline's last scheduled departure on this route that day, on days it flies the route at least twice; past 12 months. Times are typical scheduled times over the latest three months.
By month
Each calendar month pooled over 2023–2026. Best: March (91%). Worst: June (69%).
By day of week
| Day | Flights | On time | Cancelled |
|---|---|---|---|
| Monday | 140 | 80% | 0.0% |
| Tuesday | 109 | 92% | 0.9% |
| Wednesday | 109 | 90% | 0.0% |
| Thursday | 136 | 76% | 0.0% |
| Friday | 140 | 88% | 0.7% |
| Saturday | 113 | 81% | 0.0% |
| Sunday | 136 | 83% | 0.7% |
Why flights were late
Share of delay minutes on flights 15+ minutes late, as reported to BTS by the airlines.
Cancellations: weather 3
Month by month
Flight numbers on this route
Regular flights with at least 120 scheduled trips in the past year. Sorted by departure time.
| Flight | Departs | Flights | On time | Cancelled | Typical arrival | Operated by |
|---|---|---|---|---|---|---|
| AS 618 | 7:55 a.m. | 163 | 91% | 0.6% | −16 min | Alaska Airlines |
| AS 615 | 6:04 p.m. | 151 | 83% | 0.7% | −13 min | Alaska Airlines |
Worst days in the past year
| Date | Flights | On time | Cancelled |
|---|---|---|---|
| May 30, 2026 | 3 | 0% | 0 |
| May 13, 2026 | 3 | 0% | 0 |
| Jul 5, 2026 | 4 | 25% | 0 |
| Aug 24, 2026 | 4 | 25% | 0 |
| Aug 27, 2026 | 4 | 25% | 0 |
Questions
How often are flights from SEA to STL on time?
84% of 883 scheduled flights from Seattle, WA to St. Louis, MO arrived within 15 minutes of schedule between September 2025 and August 2026. 0.3% were cancelled.
What is the best time of day to fly SEA to STL?
Flights scheduled to leave at 7 a.m. were the most reliable (95% on time). The 6 p.m. departures were the least (81%).
Which airline is most on time from SEA to STL?
Alaska Airlines: 85% of its 780 flights on the route arrived on time. Southwest Airlines: 73%.
What month has the most delays from SEA to STL?
June (69% on time). The best month is March (91%), over 2023–2026.
Is the last flight of the day from SEA to STL more likely to be cancelled?
Yes. Each airline's last SEA–STL flight of the day was cancelled 0.3% of the time over the past year, against 0.0% for its earlier flights. If the last flight is cancelled, the next one is usually the following morning.
Related
- STL → SEA (return)
- Seattle-Tacoma (SEA) delays by hour
- Flights into St. Louis Lambert (STL)
- Alaska Airlines on-time record
- Southwest Airlines on-time record
- Connecting off this flight? Check the risk
Domestic flights by the airlines that report to the U.S. DOT, plus their regional partners. "On time" means arriving less than 15 minutes after schedule; cancelled and diverted flights count as not on time. Past performance is a guide, not a forecast. Method.