Best Time to Fly SEA to STL: On-Time Stats by Hour & Airline
Seattle/Tacoma International → St Louis Lambert International
Data through July 2026 · Last updated October 18, 2026
Over the last 12 months, 83.0% of Seattle (SEA) to St. Louis (STL) flights arrived on time (883 scheduled flights). That is 5.4 points above the national average of 77.6%.
Among 2 airlines, Alaska Airlines led with 84.4% on time and Southwest Airlines was last with 72.5%.
Over 24 months, Sunday was the most reliable day (82% on time) and August the worst month (67%).
The cancellation rate was 0.3% (US average 1.8%).
SEA to STL 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 |
|---|---|---|---|---|
| Alaska Airlines | 84.4% | 47 min | 0.3% | 780 |
| Southwest Airlines | 72.5% | 43 min | 1.0% | 103 |
80%+ good 70–79.9% fair <70% poor
Best time of day to fly SEA to STL
On-time arrival % by scheduled departure hour (local time), 1,758 flights over 24 months.
Show the numbers
| Departure hour | On time | Cancelled | Flights |
|---|---|---|---|
| 7am–8am | 91.3% | 0.7% | 270 |
| 8am–9am | 86.1% | 0.0% | 303 |
| 9am–10am | 85.2% | 0.5% | 192 |
| 10am–11am | Limited data | 21 | |
| 11am–12pm | 57.2% | 0.0% | 168 |
| 12pm–1pm | 65.2% | 0.0% | 178 |
| 1pm–2pm | 88.5% | 0.0% | 52 |
| 5pm–6pm | 91.2% | 0.0% | 57 |
| 6pm–7pm | 76.5% | 0.4% | 517 |
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 STL
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) | Limited data | 26 | ||
| Christmas & New Year (Dec 20 - Jan 3) | 86.7% | +4.1 pts | 0.0% | 60 |
| Summer peak (Jun 15 - Aug 15) | 69.1% | -13.5 pts | 0.2% | 487 |
| All other days | 82.6% | — | 0.3% | 1,185 |
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).