Route profile
SEA→STL
Flight reliability, delays and best times to fly from Seattle to St. Louis, 1,709 miles.
Right now
Aviation weather is not currently a factor.
Aviation weather is not currently a factor.
Route reliability
July 2023 – July 2026
Better than 82% of comparable major US routes (4,598 compared)
Calculated from 2,716 flights. How this is calculated
SEA → STL arrives on time 78.2% of the time; the return trip, STL → SEA, arrives on time 79.7% of the time.
SEA → STL spends 30.9 minutes on the ground on a 1,709-mile trip: 23.9 minutes from pushback to wheels-up at SEA and 7.0 minutes from touchdown to gate at STL.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
What stands out
Every day of the week performs about the same on this route, steadier than 97% of 4,467 comparable routes.
79.4% on time on the best day (Sunday) against 75.7% on the worst (Thursday).
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Ranked against every other route with the same kind of figure and at least 4,467 in the comparison.
What sets this route apart
Where SEA to STL differs most from similar routes by hour, weekday, month and airline, July 2023 – July 2026.
SEA to STL struggles most at 11 AM: 56.8% of its flights scheduled then arrive on time, 21.4 points behind the 78.2% on routes of similar length at the same hour. Against all other routes the gap is 24.2 points.
SEA to STL is at its best against routes of similar length for flights scheduled at 6 PM: 76.2% arrive on time, 6.3 points ahead of the 69.9% those routes manage at that hour. Against all other routes the gap is 7.6 points.
March is kinder to SEA to STL than to routes of similar length: 91.8% on time against 78.3%, 13.5 points better. Against all other routes the gap is 13.9 points.
In August, SEA to STL runs 8.1 points below routes of similar length, 67.7% on time to 75.8%. Against all other routes the gap is 8.8 points.
Alaska Airlines does better on SEA to STL than on its routes of similar length: 80.2% on time here, 76.7% there, 3.5 points apart. Against all other routes the gap is 2.2 points.
SEA to STL against comparable routes
July 2023 – July 2026| Measure | This route | Compared with | Them | Gap | Flights behind it |
|---|---|---|---|---|---|
| Hour: 11 AM departures | 56.8% | routes of similar length | 78.2% | −21.4 pts | 190 here, 82,602 there |
| Hour: 6 PM departures | 76.2% | routes of similar length | 69.9% | +6.3 pts | 821 here, 82,324 there |
| Month: March | 91.8% | routes of similar length | 78.3% | +13.5 pts | 159 here, 111,943 there |
| Month: August | 67.7% | routes of similar length | 75.8% | −8.1 pts | 313 here, 118,970 there |
| Airline: Alaska Airlines | 80.2% | routes of similar length | 76.7% | +3.5 pts | 2,423 here, 79,363 there |
Each comparison pools the flights of other routes, with this route’s own left out. Similar length means within 15% of this route’s 1,709 miles, with at least 5 such routes. A bucket is set against the most comparable group that has enough flights: similar length, then the same origin (at least 3 routes), then all other routes. Hours, weekdays and months appear only where both sides have 120 completed flights, and airlines where both have 600. The gap must be at least 2 points and 2 standard errors, and only the largest gap each way is kept per measure. These are differences in the flights counted, not causes.
When it goes wrong
July 2023 – July 2026
33 min late
against a median of 2 min early
Percentiles over 2,716 operations; cancelled and diverted flights are counted separately.
Will your connection be tight enough?
Layovers at STL after arriving from SEA.
| Connection time | Chance of missing | Reads as |
|---|---|---|
| 30 min | 43% | Likely to miss |
| 45 min | 21% | High risk |
| 60 min | 11% | Some risk |
| 90 min | 3.4% | Low risk |
| 120 min | 1.6% | Low risk |
This is one leg of a connection. Gate changes and the next flight's own schedule matter too. And a connection can fail before delay is even the question — this route cancels 0.41% of the time and diverts 0.29% of the time, which a late arrival never shows up in.
Chance of missing is the share of 2,697 arrivals on this route that landed later than the connection time less 30 minutes to reach the next gate.
The worst tenth of arrivals on this route land at least 33 minutes late (90th-percentile gate arrival delay), over 2,716 operations.
Any other layover length: connection checker.
Best time to fly
SEA → STL flights departing 5–9 AM arrived on time 86.3% of the time, against 69.8% for 12–3 PM departures, a gap of 16.5 percentage points.
By departure window
By departure hour
- 12 AM to 6 AM: too few flights to score
- 7 AM: 87.8% on time from 526 flights
- 8 AM: 84.5% on time from 407 flights
- 9 AM: 82.5% on time from 249 flights
- 10 AM: too few flights to score
- 11 AM: 56.8% on time from 192 flights
- 12 PM: 65.3% on time from 298 flights
- 1 PM to 5 PM: too few flights to score
- 6 PM: 76.2% on time from 824 flights
- 7 PM to 11 PM: too few flights to score
Departure windows with fewer than 120 flights are not scored.
Why SEA → STL runs late
July 2023 – July 2026
crew, maintenance, boarding and fueling, all within the carrier’s control
the inbound aircraft was late, so this flight started late
airspace and airport capacity, including weather-driven flow control
weather severe enough to stop this flight specifically
screening or terminal security incidents
Share of the delay minutes US DOT attributed to each cause for SEA → STL. Only delays of 15 minutes or more are attributed.
Airlines on this route
Carriers with at least 200 flights, by the airline that operated each one.
| Carrier | Flights | On time | Cancelled | Median delay | Severe |
|---|---|---|---|---|---|
| Alaska Airlines | 2,439 | 80.2% | 0.41% | -3 min | 3.1% |
| Southwest Airlines | 277 | 60.2% | 0.36% | 9 min | 6.2% |
Alaska Airlines flew 89.8% of the 2,716 flights listed.
Alaska Airlines arrived on time 20.0 percentage points more often than Southwest Airlines on this route.
Weekly and seasonal patterns
By day of week
Sunday is historically the most reliable day and Thursday the least, a gap of 3.7 percentage points.
By month
- Jan to Feb: no data
- Mar: 91.8%
- Apr: 91.0%
- May: 79.2%
- Jun: 70.0%
- Jul: 72.2%
- Aug: 67.7%
- Sep: 78.3%
- Oct: 83.7%
- Nov: 79.7%
- Dec: 84.1%
August is historically the weakest month and March the strongest, a spread of 24.1 percentage points.
Reliability over time
July 2023 – July 2026
- July 2023: too few flights to score (91)
- August 2023: too few flights to score (93)
- September 2023: too few flights to score (89)
- October 2023: too few flights to score (63)
- November 2023: too few flights to score (58)
- December 2023: too few flights to score (56)
- January 2024: too few flights to score (37)
- February 2024: too few flights to score (38)
- March 2024: too few flights to score (56)
- April 2024: too few flights to score (60)
- May 2024: too few flights to score (78)
- June 2024: too few flights to score (117)
- July 2024: 64.8% from 122 flights
- August 2024: too few flights to score (110)
- September 2024: too few flights to score (100)
- October 2024: too few flights to score (60)
- November 2024: too few flights to score (50)
- December 2024: too few flights to score (54)
- January 2025: too few flights to score (34)
- February 2025: too few flights to score (38)
- March 2025: too few flights to score (52)
- April 2025: too few flights to score (59)
- May 2025: too few flights to score (79)
- June 2025: too few flights to score (116)
- July 2025: 63.9% from 123 flights
- August 2025: too few flights to score (111)
- September 2025: too few flights to score (98)
- October 2025: too few flights to score (61)
- November 2025: too few flights to score (50)
- December 2025: too few flights to score (54)
- January 2026: too few flights to score (37)
- February 2026: too few flights to score (38)
- March 2026: too few flights to score (52)
- April 2026: too few flights to score (60)
- May 2026: too few flights to score (81)
- June 2026: too few flights to score (118)
- July 2026: 84.4% from 123 flights
Over the most recent 12 months (2025-08 to 2026-07), on-time arrivals averaged 83.1% against 75.1% in the 12 months before — improving by 8.0 percentage points.
Data and methodology
Calculated by FlyerIntel from 2,716 SEA → STL flight records from the US DOT Bureau of Transportation Statistics, covering July 2023 – July 2026. Late means 15 or more minutes past scheduled arrival; cancelled and diverted flights are left out of on-time rates.
Full methodology · Data sources · Report a problem
Related research: How Long a Layover Needs to Be · Two Airlines on One Route · Best Time of Day to Fly From Major US Airports
Analysis last recomputed