Carrier route record
ASDEN→SEA
Alaska Airlines · Denver to Seattle
- Flights
- 1,558
- Period
- July 2025 to June 2026
- Share of route
- 25%
- Carriers
- 6
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Alaska Airlines.
Alaska on DEN to SEA sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, 4 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 1,558 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,903 at 80.0% on time.
United Airlines is the most reliable of the four carriers covered here at 80.0% on time across 1,903 flights.
Key figures
On time
73.8%
Arrivals under 15 minutes late, of 1,543 completed flights
Avg delay
57 min
Across delayed arrivals only, not all flights
Cancelled
0.96%
National rate is 1.81%
Whole route
73.9%
Every carrier on DEN to SEA, 6,309 flights
These figures cover 1,558 flights between July 2025 and June 2026. The median arrival is 3 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 DEN to SEA
Alaska flew 1,558 of the 6,309 flights on DEN to SEA, about 25% of it. Its 73.8% on time is about level with the route as a whole at 73.9%. Ranked by on-time rate it is number five of six carriers on the route, where the range runs from United at 80.0% to Southwest at 61.7%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The choice of carrier is not cosmetic here. United Airlines arrives on time 80.0% of the time; Southwest Airlines manages 61.7%. Sample sizes sit next to every figure, because a two-point gap across 1,341 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,903 | 80.0% | 55 min | 0.63% | B+ |
| Delta Air Lines | 868 | 79.2% | 89 min | 0.92% | B+ |
| SkyWest Airlinesthin sample | 220 | 75.8% | 70 min | 0.45% | B+ |
| Frontier Airlines | 419 | 74.9% | 60 min | 1.91% | C |
| Alaska Airlines (this page) | 1,558 | 73.8% | 57 min | 0.96% | C+ |
| Southwest Airlines | 1,341 | 61.7% | 47 min | 0.30% | D+ |
The spread between United and Southwest is 18 points, wide enough that it should decide the booking. On a hundred trips that is 18 more arrivals inside the on-time window.
Flight by flight
Alaska flight numbers on DEN to SEA
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 33 points, against 18 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am294 flights88.1%
- 8am–11am218 flights80.0%
- 11am–2pm345 flights80.7%
- 2pm–5pm244 flights65.6%
- 5pm–8pm294 flights63.4%
- 8pm–5am163 flights55.3%
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 55.3% on time, against 88.1% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 11am–2pm window is the busiest, with 345 flights scheduled in it.
Across the year
Alaska on DEN to SEA through the year
July is the worst month at 55.8% on time, 31 points below February, the best at 87.0%. 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 176 flights.
Across the week, Saturday is the strongest day at 81.7% on time and Thursday the weakest at 65.9%. 16 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Alaska runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 47% of the 23,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 47%Late-arriving aircraft
- 28%Carrier
- 22%National Airspace System
- 3%Extreme weather
- 0%Security
47% 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 23,000 reported delay minutes here, that single category outweighs weather by 16 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 22,993 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 88.1% on time here.
Cancellations sit at 0.96% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
7.2% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.
The 1,024 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg runs 75.9% on time across 1,558 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.
The sample behind these figures is 1,558 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
What to do with this
Booking Alaska on DEN to SEA
Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 87.0% on time and July 55.8%, a swing of 31 points. If the dates move at all, move them out of July before you think about anything else. 1,543 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to SEA, every carrier
- Alaska on SEA to DEN, the return leg
- United Airlines on DEN to SEA80.0%
- Delta Air Lines on DEN to SEA79.2%
- SkyWest Airlines on DEN to SEA75.8%
- Frontier Airlines on DEN to SEA74.9%
- Southwest Airlines on DEN to SEA61.7%
- Alaska Airlines network-wide record
- Denver International (DEN) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
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.