Carrier route record
UASEA→DEN
United Airlines · Seattle to Denver
- Flights
- 1,905
- Period
- July 2025 to June 2026
- Share of route
- 30%
- Carriers
- 6
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.
United on SEA to DEN earns an A+. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 10 points better than the national rate of 77.6%. When something does go wrong the average delay runs a little over an hour. That rests on 1,905 flights. The strongest carrier on the route with a full sample, Alaska Airlines, flew 1,558 at 75.9% on time.
Set against the rest of the country, United's SEA to DEN record is 10 points better than the US average of 77.6%. That gap is worth roughly 99 fewer late arrivals for every thousand flights.
Key figures
On time
87.5%
Arrivals under 15 minutes late, of 1,876 completed flights
Avg delay
73 min
Across delayed arrivals only, not all flights
Cancelled
0.84%
National rate is 1.81%
Whole route
77.8%
Every carrier on SEA to DEN, 6,317 flights
These figures cover 1,905 flights between July 2025 and June 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.
Carrier by carrier
United against every carrier on SEA to DEN
United flew 1,905 of the 6,317 flights on SEA to DEN, about 30% of it. Its 87.5% on time is 10 points better than the route as a whole, which runs 77.8%. Ranked by on-time rate it is first 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. Alaska Airlines arrives on time 75.9% 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 (this page) | 1,905 | 87.5% | 73 min | 0.84% | A+ |
| SkyWest Airlinesthin sample | 221 | 85.0% | 60 min | 0.45% | A+ |
| Alaska Airlines | 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+ |
Alaska leads Southwest by 7 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
United flight numbers on SEA to DEN
Departure window
When United 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 7 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am349 flights98.0%
- 8am–11am364 flights90.3%
- 11am–2pm522 flights87.1%
- 2pm–5pm459 flights78.8%
- 5pm–8pm181 flights85.6%
- 8pm–5am30 flights80.0%
Scale runs 70% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 98.0% of the time, against 78.8% for the afternoon window. That is 19 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 522 flights scheduled in it.
Across the year
United on SEA to DEN through the year
July is the worst month at 75.4% on time, 20 points below April, the best at 95.7%. 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 200 flights.
Across the week, Saturday is the strongest day at 90.8% on time and Friday the weakest at 82.5%. 8 points is a smaller lever than departure hour, but it is free.
Delay causes
Why United 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 17,000 reported delay minutes.
- 41%Late-arriving aircraft
- 32%National Airspace System
- 24%Carrier
- 3%Extreme weather
- 0%Security
41% 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 17,000 reported delay minutes here, that single category outweighs weather by 12 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 17,161 reported delay minutes.
32% 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 5,504 minutes out of 17,000, against a national NAS share of 21%.
Cancellations are rare at 0.84%, 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 4.4% 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.
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 is a different operation and performs like one: it runs 80.0% on time across 1,903 flights, 8 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 8 points of difference.
The sample behind these figures is 1,905 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 United on SEA to DEN
Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 95.7% on time and July 75.4%, a swing of 20 points. If the dates move at all, move them out of July before you think about anything else. 1,876 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to DEN, every carrier
- United on DEN to SEA, the return leg
- SkyWest Airlines on SEA to DEN85.0%
- Alaska Airlines on SEA to DEN75.9%
- Frontier Airlines on SEA to DEN74.9%
- Delta Air Lines on SEA to DEN73.3%
- Southwest Airlines on SEA to DEN69.0%
- United Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Denver International (DEN) 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.