Best Time to Fly STL to SEA: On-Time Stats by Hour & Airline
St Louis Lambert International → Seattle/Tacoma International
Data through July 2026 · Last updated October 18, 2026
Over the last 12 months, 79.1% of St. Louis (STL) to Seattle (SEA) flights arrived on time (884 scheduled flights). That is 1.4 points above the national average of 77.6%.
Among 2 airlines, Alaska Airlines led with 82.5% on time and Southwest Airlines was last with 53.4%.
Over 24 months, Wednesday was the most reliable day (82% on time) and June the worst month (67%).
The cancellation rate was 0.9% (US average 1.8%).
STL to SEA 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 | 82.5% | 51 min | 1.0% | 781 |
| Southwest Airlines | 53.4% | 39 min | 0.0% | 103 |
80%+ good 70–79.9% fair <70% poor
Best time of day to fly STL to SEA
On-time arrival % by scheduled departure hour (local time), 1,759 flights over 24 months.
Show the numbers
| Departure hour | On time | Cancelled | Flights |
|---|---|---|---|
| 6am–7am | 92.3% | 0.4% | 274 |
| 7am–8am | 86.4% | 0.8% | 370 |
| 9am–10am | Limited data | 9 | |
| 10am–11am | Limited data | 25 | |
| 11am–12pm | 59.2% | 0.0% | 49 |
| 12pm–1pm | 58.5% | 0.0% | 41 |
| 1pm–2pm | Limited data | 12 | |
| 2pm–3pm | 88.2% | 1.0% | 299 |
| 3pm–4pm | 75.8% | 0.0% | 304 |
| 4pm–5pm | 82.8% | 3.1% | 96 |
| 5pm–6pm | 38.7% | 0.0% | 31 |
| 6pm–7pm | 62.7% | 0.0% | 59 |
| 7pm–8pm | 62.2% | 1.1% | 190 |
Best day of the week
24 months, by day of departure.
Best month to fly
24 months, by calendar month.
Holiday travel on STL to SEA
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) | 78.3% | -4.3 pts | 0.0% | 60 |
| Summer peak (Jun 15 - Aug 15) | 69.6% | -13.0 pts | 0.6% | 487 |
| All other days | 82.6% | — | 0.6% | 1,186 |
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).