Carrier route record
UAIAD→DEN
United Airlines · Washington to Denver
- Flights
- 2,798
- Period
- July 2025 to June 2026
- Share of route
- 79%
- Carriers
- 2
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.
United on IAD to DEN lands a B+, 6 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 a little over an hour on average. That is a workable record, not a spotless one. That rests on 2,798 flights, with a median arrival 8 minutes early.
Set against the rest of the country, United's IAD to DEN record is 6 points better than the US average of 77.6%. That gap is worth roughly 56 fewer late arrivals for every thousand flights.
Key figures
On time
83.2%
Arrivals under 15 minutes late, of 2,761 completed flights
Avg delay
71 min
Across delayed arrivals only, not all flights
Cancelled
0.46%
National rate is 1.81%
Whole route
81.7%
Every carrier on IAD to DEN, 3,560 flights
These figures cover 2,798 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
United against every carrier on IAD to DEN
United flew 2,798 of the 3,560 flights on IAD to DEN, most of the route. Its 83.2% on time is 2 points better than the route as a whole, which runs 81.7%. Ranked by on-time rate it is first of two carriers on the route, where the range runs from United at 83.2% to Southwest at 76.2%.
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 |
|---|---|---|---|---|---|
| United Airlines (this page) | 2,798 | 83.2% | 71 min | 0.46% | B+ |
| Southwest Airlines | 762 | 76.2% | 53 min | 1.18% | B |
Flight by flight
United flight numbers on IAD 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 21 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–8am111 flights91.7%
- 8am–11am730 flights88.4%
- 11am–2pm365 flights91.4%
- 2pm–5pm726 flights82.3%
- 5pm–8pm403 flights70.5%
- 8pm–5am463 flights79.3%
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 91.7% of the time, against 70.5% for the evening window. That is 21 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 730 flights scheduled in it.
Across the year
United on IAD to DEN through the year
July is the worst month at 69.3% on time, 23 points below November, the best at 92.7%. 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 277 flights.
Across the week, Tuesday is the strongest day at 84.8% on time and Thursday the weakest at 79.3%. 6 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 33,000 reported delay minutes.
- 38%Late-arriving aircraft
- 28%National Airspace System
- 25%Carrier
- 9%Extreme weather
38% 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 33,000 reported delay minutes here, that single category outweighs weather by 4 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 32,993 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 91.7% on time here.
Cancellations are rare at 0.46%, 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 a little over an hour, which a normal layover absorbs.
The 1,452 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 84.4% on time across 2,797 flights, within about a point 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 2,798 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 IAD to DEN
Put together: the calendar is the biggest lever here, not the carrier or the hour. November runs 92.7% on time and July 69.3%, a swing of 23 points. If the dates move at all, move them out of July before you think about anything else. 2,761 completed flights over 12 months sit behind that.
Related
Where to go next
- IAD to DEN, every carrier
- United on DEN to IAD, the return leg
- Southwest Airlines on IAD to DEN76.2%
- United Airlines network-wide record
- Washington Dulles International (IAD) 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.