Carrier route record
UADEN→SEA
United Airlines · Denver to Seattle
- Flights
- 1,903
- 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 DEN to SEA lands a B+, 2 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 1,903 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 868 at 79.2% on time.
The US average over the same twelve months is 77.6%, so there is little to separate United on DEN to SEA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
80.0%
Arrivals under 15 minutes late, of 1,891 completed flights
Avg delay
55 min
Across delayed arrivals only, not all flights
Cancelled
0.63%
National rate is 1.81%
Whole route
73.9%
Every carrier on DEN to SEA, 6,309 flights
These figures cover 1,903 flights between July 2025 and June 2026. The median arrival is 5 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 DEN to SEA
United flew 1,903 of the 6,309 flights on DEN to SEA, about 30% of it. Its 80.0% on time is 6 points better than the route as a whole, which runs 73.9%. Ranked by on-time rate it is first 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. Delta Air Lines arrives on time 79.2% 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 (this page) | 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 | 1,558 | 73.8% | 57 min | 0.96% | C+ |
| Southwest Airlines | 1,341 | 61.7% | 47 min | 0.30% | D+ |
The spread between Delta 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
United flight numbers on DEN to SEA
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 24 points, against 18 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am233 flights93.1%
- 8am–11am205 flights88.1%
- 11am–2pm397 flights84.1%
- 2pm–5pm475 flights79.9%
- 5pm–8pm364 flights68.9%
- 8pm–5am229 flights69.8%
Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 93.1% of the time, against 68.9% for the evening window. That is 24 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 475 flights scheduled in it.
Across the year
United on DEN to SEA through the year
November is the best month on the calendar at 91.1% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. July was the busiest month here, with 200 flights.
Across the week, Tuesday is the strongest day at 82.8% on time and Friday the weakest at 77.3%. 6 points is a smaller lever than departure hour, but it is free.
Delay causes
Why United runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 44% of the 21,000 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.
- 44%Late-arriving aircraft
- 31%Carrier
- 22%National Airspace System
- 2%Extreme weather
44% 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 21,000 reported delay minutes here, that single category outweighs weather by 19 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 21,001 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 93.1% on time here.
Cancellations are rare at 0.63%, 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
6.0% 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 is a different operation and performs like one: it runs 87.5% on time across 1,905 flights, 8 points above 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 1,903 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 DEN to SEA
Put together: the calendar is the biggest lever here, not the carrier or the hour. November runs 91.1% on time and March 70.3%, a swing of 21 points. If the dates move at all, move them out of March before you think about anything else. 1,891 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to SEA, every carrier
- United on SEA to DEN, the return leg
- Delta Air Lines on DEN to SEA79.2%
- SkyWest Airlines on DEN to SEA75.8%
- Frontier Airlines on DEN to SEA74.9%
- Alaska Airlines on DEN to SEA73.8%
- Southwest Airlines on DEN to SEA61.7%
- United 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.