Carrier route record
UAIAD→DEN
United Airlines · Washington to Denver
- Flights
- 2,791
- Period
- September 2025 to August 2026
- Share of route
- 82%
- Carriers
- 2
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with United Airlines.
United on IAD to DEN earns a B+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.3%. When something does go wrong the average delay runs about an hour. That rests on 2,791 flights, with a median arrival 9 minutes early.
Set against the rest of the country, United's IAD to DEN record is 7 points better than the US average of 77.3%. That gap is worth roughly 68 fewer late arrivals for every thousand flights.
Key figures
On time
84.1%
Arrivals under 15 minutes late, of 2,758 completed flights
Avg delay
68 min
Across delayed arrivals only, not all flights
Cancelled
0.50%
National rate is 1.89%
Whole route
83.1%
Every carrier on IAD to DEN, 3,387 flights
These figures cover 2,791 flights between September 2025 and August 2026. The median arrival is 9 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.
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Carrier by carrier
United against every carrier on IAD to DEN
United flew 2,791 of the 3,387 flights on IAD to DEN, most of the route. Its 84.1% on time is about level with the route as a whole at 83.1%. Ranked by on-time rate it is first of two carriers on the route, where the range runs from United at 84.1% to Southwest at 78.4%.
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) | 2,791 | 84.1% | 68 min | 0.50% | B+ |
| Southwest Airlines | 596 | 78.4% | 48 min | 1.01% | B |
Flight by flight
United flight numbers on IAD to DEN
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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 27 points, against half a point between the best and worst carrier.
- 5am–8am115 flights96.5%
- 8am–11am730 flights89.3%
- 11am–2pm365 flights91.2%
- 2pm–5pm727 flights81.4%
- 5pm–8pm439 flights69.7%
- 8pm–5am415 flights85.0%
Scale runs 60% to 100%.
Book the early departure. Flights leaving between 5am–8am arrive on time 96.5% of the time, against 69.7% for the evening window. That is 27 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
August is the worst month at 75.0% on time, 18 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 266 flights.
Across the week, Tuesday is the strongest day at 87.4% on time and Thursday the weakest at 80.0%, a spread of 7 points.
Arrival by arrival
How late United on IAD to DEN runs when it is late
United on IAD to DEN often beats the schedule: 945 of 2,758 completed flights, 34%, arrived 15 minutes or more early. The 439 late arrivals split 173 under half an hour, 109 between 30 and 60 minutes, and 157 an hour or more.
- 15+ min early945 flights34.3%
- Within 15 min1,374 flights49.8%
- 15–29 min late173 flights6.3%
- 30–59 min late109 flights4.0%
- 1–2 hours late95 flights3.4%
- 2+ hours late62 flights2.2%
Scale runs 0% to 100%.
Share of 2,758 completed flights by arrival against schedule.
A late pushback is often recovered here: of 423 departures that left 15 minutes late or more, 133 still arrived on time. In the other direction, 149 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at DEN.
The worst days
Worst days for United on IAD to DEN
The latest arrival of the period was on 16 July 2026, 9 hours 58 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 16 July 2026 | 9 hours 58 minutes | Late-arriving aircraft |
| 27 January 2026 | 9 hours 23 minutes | Carrier |
| 31 December 2025 | 8 hours 54 minutes | Late-arriving aircraft |
| 12 June 2026 | 8 hours 45 minutes | Late-arriving aircraft |
| 6 June 2026 | 8 hours 9 minutes | Late-arriving aircraft |
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 30,000 reported delay minutes.
- 35%Late-arriving aircraft
- 34%National Airspace System
- 23%Carrier
- 8%Extreme weather
35% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 30,000 reported delay minutes here, that single category outweighs weather by 4 to one. The split is drawn from 29,776 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 9,984 minutes out of 30,000, against a national NAS share of 21%.
Cancellations are rare at 0.50%, below the national 1.89% 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
5.7% of arrivals land an hour or more late, close to the national 8.3%, so 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 1,452 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.
The return leg runs 84.8% on time across 2,790 flights, within half 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 2,791 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 August 75.0%, a swing of 18 points. If the dates move at all, move them out of August before you think about anything else. 2,758 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 DEN78.4%
- 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 7.05 million flight records
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.