Carrier route record
ASSEA→STL
Alaska Airlines · Seattle to St. Louis
- Flights
- 780
- Period
- September 2025 to August 2026
- Share of route
- 88%
- Carriers
- 2
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Alaska Airlines.
Alaska on SEA to STL earns an A+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 9 points better than the national rate of 77.3%. When something does go wrong the average delay runs roughly 50 minutes. That rests on 780 flights, with a median arrival 12 minutes early.
Set against the rest of the country, Alaska's SEA to STL record is 9 points better than the US average of 77.3%. That gap is worth roughly 85 fewer late arrivals for every thousand flights.
Key figures
On time
85.8%
Arrivals under 15 minutes late, of 776 completed flights
Avg delay
48 min
Across delayed arrivals only, not all flights
Cancelled
0.26%
National rate is 1.89%
Whole route
84.4%
Every carrier on SEA to STL, 883 flights
These figures cover 780 flights between September 2025 and August 2026. The median arrival is 12 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
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Carrier by carrier
Alaska against every carrier on SEA to STL
Alaska flew 780 of the 883 flights on SEA to STL, most of the route. Its 85.8% on time is about level with the route as a whole at 84.4%. Ranked by on-time rate it is first of two carriers on the route, where the range runs from Alaska at 85.8% to Southwest at 73.5%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Alaska Airlines (this page) | 780 | 85.8% | 48 min | 0.26% | A+ |
| Southwest Airlinesthin sample | 103 | 73.5% | 55 min | 0.97% | C+ |
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Departure window
When Alaska runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 12 points, against half a point between the best and worst carrier.
- 5am–8am—
- 8am–11am358 flights90.7%
- 11am–2pm144 flights78.5%
- 2pm–5pm—
- 5pm–8pm278 flights83.4%
- 8pm–5am—
Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.
The weak window here is the middle of the day, not the evening: 11am–2pm runs 78.5% on time against 90.7% for 8am–11am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 8am–11am window is the busiest, with 358 flights scheduled in it.
Across the year
Alaska on SEA to STL through the year
August is the worst month at 77.3% on time, 23 points below April, the best at 100.0%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. July was the busiest month here, with 92 flights.
Across the week, Tuesday is the strongest day at 93.1% on time and Thursday the weakest at 77.1%, a spread of 16 points.
Arrival by arrival
How late Alaska on SEA to STL runs when it is late
Alaska on SEA to STL often beats the schedule: 338 of 776 completed flights, 44%, arrived 15 minutes or more early. Most of the lateness is short. 55 of the 110 late arrivals were under half an hour behind, and 18 reached an hour or more.
- 15+ min early338 flights43.6%
- Within 15 min328 flights42.3%
- 15–29 min late55 flights7.1%
- 30–59 min late37 flights4.8%
- 1–2 hours late10 flights1.3%
- 2+ hours late8 flights1.0%
Scale runs 0% to 100%.
Share of 776 completed flights by arrival against schedule.
33 of 122 late departures made up the time and arrived on time, 27% of them. 21 flights left on time and still arrived late.
The worst days
Worst days for Alaska on SEA to STL
The latest arrival of the period was on 23 October 2025, 5 hours 29 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The five worst days are spread across October, December, August, July and May, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 23 October 2025 | 5 hours 29 minutes | Carrier |
| 19 December 2025 | 4 hours 45 minutes | Late-arriving aircraft |
| 7 August 2026 | 3 hours 36 minutes | Carrier |
| 16 July 2026 | 3 hours 30 minutes | Extreme weather |
| 14 May 2026 | 3 hours 6 minutes | Late-arriving aircraft |
Delay causes
Why Alaska runs late on this route
Carrier accounts for 50% of the 5,319 delay minutes carriers reported here, and the remaining four split what is left.
- 50%Carrier
- 32%Late-arriving aircraft
- 13%National Airspace System
- 5%Extreme weather
The largest share of delay minutes, 50%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 2,642 of the 5,319 delay minutes reported here. The split is drawn from 5,319 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 90.7% on time here.
Cancellations are rare at 0.26%, below the national 1.89% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here costs
Badly late arrivals are rare here: only 2.3% land an hour or more behind schedule, against 8.3% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
At 1,709 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.
The return leg is a different operation and performs like one: it runs 82.5% on time across 781 flights, 3 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 3 points of difference.
One caution: this is a thin sample. 780 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Alaska on SEA to STL
Put together: treat all of this as provisional. 780 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 85.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 776 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to STL, every carrier
- Alaska on STL to SEA, the return leg
- Southwest Airlines on SEA to STL73.5%
- Alaska Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- St. Louis Lambert International (STL) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.