Carrier route record
ASSEA→DEN
Alaska Airlines · Seattle to Denver
- 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 SEA to DEN sits in the middle of the pack with a B+. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.6%. The late ones land about 50 minutes behind schedule. That rests on 1,558 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,905 at 87.5% on time.
United Airlines is the most reliable of the four carriers covered here at 87.5% on time across 1,905 flights.
Key figures
On time
75.9%
Arrivals under 15 minutes late, of 1,541 completed flights
Avg delay
50 min
Across delayed arrivals only, not all flights
Cancelled
0.83%
National rate is 1.81%
Whole route
77.8%
Every carrier on SEA to DEN, 6,317 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 SEA to DEN
Alaska flew 1,558 of the 6,317 flights on SEA to DEN, about 25% of it. Its 75.9% on time is 2 points worse than the route as a whole, which runs 77.8%. Ranked by on-time rate it is number three of six carriers on the route, where the range runs from United at 87.5% to Southwest at 69.0%. 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 87.5% of the time; Southwest Airlines manages 69.0%. Sample sizes sit next to every figure, because a two-point gap across 1,345 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,905 | 87.5% | 73 min | 0.84% | A+ |
| SkyWest Airlinesthin sample | 221 | 85.0% | 60 min | 0.45% | A+ |
| Alaska Airlines (this page) | 1,558 | 75.9% | 50 min | 0.83% | B+ |
| Frontier Airlines | 419 | 74.9% | 75 min | 1.91% | C |
| Delta Air Lines | 869 | 73.3% | 58 min | 0.92% | C+ |
| Southwest Airlines | 1,345 | 69.0% | 52 min | 0.59% | C+ |
The spread between United and Southwest is 19 points, wide enough that it should decide the booking. On a hundred trips that is 19 more arrivals inside the on-time window.
Flight by flight
Alaska flight numbers on SEA to DEN
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 22 points, against 19 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am98 flights89.7%
- 8am–11am398 flights77.9%
- 11am–2pm394 flights75.7%
- 2pm–5pm200 flights68.2%
- 5pm–8pm220 flights71.4%
- 8pm–5am248 flights77.8%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 89.7% of the time, against 68.2% for the afternoon window. That is 22 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 398 flights scheduled in it.
Across the year
Alaska on SEA to DEN through the year
July is the worst month at 48.0% on time, 48 points below April, the best at 95.6%. 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 81.1% on time and Sunday the weakest at 70.9%. 10 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 18,000 reported delay minutes.
- 36%Late-arriving aircraft
- 34%National Airspace System
- 25%Carrier
- 5%Extreme weather
- 0%Security
36% 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 18,000 reported delay minutes here, that single category outweighs weather by 7 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 18,456 reported delay minutes.
34% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 6,238 minutes out of 18,000, against a national NAS share of 21%.
Cancellations are rare at 0.83%, 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
6.2% 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 50 minutes, 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 73.8% 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 SEA to DEN
Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 95.6% on time and July 48.0%, a swing of 48 points. If the dates move at all, move them out of July before you think about anything else. 1,541 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to DEN, every carrier
- Alaska on DEN to SEA, the return leg
- United Airlines on SEA to DEN87.5%
- SkyWest Airlines on SEA to DEN85.0%
- Frontier Airlines on SEA to DEN74.9%
- Delta Air Lines on SEA to DEN73.3%
- Southwest Airlines on SEA to DEN69.0%
- Alaska Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Denver International (DEN) 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.