Carrier route record
ASSEA→STL
Alaska Airlines · Seattle to St. Louis
- Flights
- 780
- Period
- July 2025 to June 2026
- Share of route
- 88%
- Carriers
- 2
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Alaska Airlines.
Alaska on SEA to STL lands a B+, 5 points better than the national rate of 77.6%. About one flight in six arrives 15 minutes late or worse, and those flights are late by roughly 45 minutes on average. That is a workable record, not a spotless one. That rests on 780 flights, with a median arrival 8 minutes early.
Set against the rest of the country, Alaska's SEA to STL record is 5 points better than the US average of 77.6%. That gap is worth roughly 46 fewer late arrivals for every thousand flights.
Key figures
On time
82.2%
Arrivals under 15 minutes late, of 776 completed flights
Avg delay
43 min
Across delayed arrivals only, not all flights
Cancelled
0.26%
National rate is 1.81%
Whole route
80.2%
Every carrier on SEA to STL, 883 flights
These figures cover 780 flights between July 2025 and June 2026. The median arrival is 8 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.
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 82.2% on time is 2 points better than the route as a whole, which runs 80.2%. Ranked by on-time rate it is first of two carriers on the route, where the range runs from Alaska at 82.2% to Southwest at 64.7%. 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 | 82.2% | 43 min | 0.26% | B+ |
| Southwest Airlinesthin sample | 103 | 64.7% | 39 min | 0.00% | D+ |
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 19 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am—
- 8am–11am358 flights88.2%
- 11am–2pm144 flights69.4%
- 2pm–5pm—
- 5pm–8pm278 flights81.2%
- 8pm–5am—
Scale runs 60% 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 69.4% on time against 88.2% 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 64.8% on time, 35 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, Sunday is the strongest day at 86.4% on time and Monday the weakest at 78.0%. 8 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Alaska runs late on this route
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 5,890 reported delay minutes.
- 41%Carrier
- 39%Late-arriving aircraft
- 19%National Airspace System
- 0%Extreme weather
39% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 5,890 reported delay minutes here, that single category outweighs weather by 39 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 5,890 reported delay minutes.
The largest share of delay minutes, 41%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 2,433 of the 5,890 delay minutes reported here.
Cancellations are rare at 0.26%, below the national 1.81% 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 2.7% land an hour or more behind schedule, against 8.1% 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 runs 80.7% on time across 781 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
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 82.2% 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 STL64.7%
- 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 7.04 million flight records
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.