Route reliability record
DEN→IAD
Denver to Washington
- Flights
- 3,385
- Period
- September 2025 to August 2026
- Distance
- 1,452 mi
- Carriers
- 2
This route lands a B+, 5 points better than the national rate of 77.3%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 3,385 DEN to IAD flights, of which United Airlines flew 2,790 at 84.8% on time.
Best time to fly DEN to IAD: a 8pm–5am departure, ideally on a Wednesday. Flights in that window arrived on time 93.6% of the time and Wednesday flights 86.1%, against 81.8% for the route overall.
Set against the rest of the country, this route's record is 5 points better than the US average of 77.3%. That gap is worth roughly 45 fewer late arrivals for every thousand flights.
Key figures
On time
81.8%
Arrivals under 15 minutes late, of 3,364 completed flights
Avg delay
60 min
Across delayed arrivals only, not all flights
Cancelled
0.59%
National rate is 1.89%
Best carrier
United
84.8% on time across 2,790 flights
These figures cover 3,385 flights between September 2025 and August 2026. The median arrival is 7 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
Which airline is most reliable on DEN to IAD
The choice of carrier is not cosmetic here. United Airlines arrives on time 84.8% of the time; Southwest Airlines manages 67.7%. Sample sizes sit next to every figure, because a two-point gap across 595 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 2,790 | 84.8% | 66 min | 0.50% | B+ |
| Southwest Airlines | 595 | 67.7% | 47 min | 1.01% | C |
The spread between United and Southwest is 17 points, wide enough that it should decide the booking. On a hundred trips that is 17 more arrivals inside the on-time window.
Flight by flight
Flights on DEN to IAD
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly Denver to Washington
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 3 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. DEN → IADDenver to Washington | United Airlines | 84.4% | 84.8% | 0.50% | 5am–8am, Wed | UA 1924 23:59 |
| 2. DEN → BWIDenver to Baltimore | United Airlines | 81.7% | 82.2% | 0.60% | 8am–11am, Wed | UA 1362 09:46 |
| 3. DEN → DCADenver to Washington | Frontier Airlines | 76.9% | 77.5% | 0.81% | 5am–8am, Sat | F9 686 07:35 |
| 4. DEN → BWIDenver to Baltimore | Southwest Airlines | 74.0% | 74.9% | 1.15% | 5am–8am, Wed | — |
| 5. DEN → IADDenver to Washington | Southwest Airlines | 67.0% | 67.7% | 1.01% | 8am–11am, Tue | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 29 points, against 17 points between the best and worst carrier.
- 5am–8am309 flights93.2%
- 8am–11am822 flights85.2%
- 11am–2pm587 flights80.5%
- 2pm–5pm688 flights83.6%
- 5pm–8pm635 flights64.8%
- 8pm–5am344 flights93.6%
Scale runs 55% to 100%.
The 5pm–8pm window is where this operation falls apart: 64.8% on time, against 93.6% for the 8pm–5am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 8am–11am window is the busiest, with 822 flights scheduled in it.
Explore
Filter DEN to IAD by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On DEN to IAD, the best departure window is 8pm–5am at 93.6% on time and the worst is 5pm–8pm at 64.8%, a wide gap of 28.8 points. All US flights leaving 8pm–5am ran 70.1%.
- 5–8am93.2%
- 8–11am85.2%
- 11am–2pm80.5%
- 2–5pm83.6%
- 5–8pm64.8%
- 8pm–5am93.6%
best all US flightsScale 55% to 100%.
Across the year
When delays peak on this route
This route's year swings by 19 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
July is the worst month at 70.5% on time, 19 points below January, the best at 89.2%. 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. May was the busiest month here, with 316 flights.
Across the week, Wednesday is the strongest day at 86.1% on time and Sunday the weakest at 77.5%, a spread of 9 points.
Delay causes
Why this route gets delayed
Late-arriving aircraft accounts for 45% of the 37,000 delay minutes carriers reported here, and the remaining four split what is left.
- 45%Late-arriving aircraft
- 31%Carrier
- 22%National Airspace System
- 1%Extreme weather
- 1%Security
45% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 37,000 reported delay minutes here, that single category outweighs weather by 45 to one. The split is drawn from 36,509 reported delay minutes.
Cancellations are rare at 0.59%, 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 actually costs
5.6% 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 83.1% on time across 3,387 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 3,385 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.
Work out the risk of missing a connection in IAD after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 89.2% on time and July 70.5%, a swing of 19 points. If the dates move at all, move them out of July before you think about anything else. 3,364 completed flights over 12 months sit behind that.
Common questions
DEN to IAD questions
How often is DEN to IAD delayed?
Roughly one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 18.2% of the 3,385 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on DEN to IAD?
United Airlines leads at 84.8% on time across 2,790 flights. Southwest Airlines is at the other end on 67.7%, a gap of 17 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on DEN to IAD?
The 8pm–5am departure window is the strongest at 93.6% on time. The 5pm–8pm window is the weakest at 64.8%, 29 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are July delays on DEN to IAD?
July is the weakest month at 70.5% on time, compared with 89.2% in January. Across the year that is 19 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- IAD to DEN — the return legseparate record
- Denver International (DEN) delay statistics
- Washington Dulles International (IAD) delay statistics
- United Airlines on DEN to IAD84.8%
- Southwest Airlines on DEN to IAD67.7%
- DEN to PHX, a related route75.6%
- ATL to IAD, a related route76.4%
- DEN to SLC, a related route78.2%
- United Airlines on-time record84.8%
- Southwest Airlines on-time record67.7%
- Why the first flight of the morning is statistically safest
- Same route, different airline: where the carrier you pick matters most
Direction matters. DEN to IAD and IAD to DEN are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.