Route reliability record
IAD→DEN
Washington to Denver
- Flights
- 3,387
- Period
- September 2025 to August 2026
- Distance
- 1,452 mi
- Carriers
- 2
This route lands a B+, 6 points better than the national rate of 77.3%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 3,387 IAD to DEN flights, of which United Airlines flew 2,791 at 84.1% on time.
Best time to fly IAD to DEN: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 93.4% of the time and Tuesday flights 86.5%, against 83.1% for the route overall.
Set against the rest of the country, this route's record is 6 points better than the US average of 77.3%. That gap is worth roughly 58 fewer late arrivals for every thousand flights.
Key figures
On time
83.1%
Arrivals under 15 minutes late, of 3,347 completed flights
Avg delay
63 min
Across delayed arrivals only, not all flights
Cancelled
0.59%
National rate is 1.89%
Best carrier
United
84.1% on time across 2,791 flights
These figures cover 3,387 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.
Fare search by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Carrier by carrier
Which airline is most reliable on IAD to DEN
The two carriers here are closely matched: 6 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 2,791 | 84.1% | 68 min | 0.50% | B+ |
| Southwest Airlines | 596 | 78.4% | 48 min | 1.01% | B |
No carrier stands out. United tops the table at 84.1%, 6 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Flights on IAD to DEN
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.
Timetable by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Best ways to make this trip
The most reliable ways to fly Washington to Denver
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. BWI → DENBaltimore to Denver | United Airlines | 84.1% | 84.5% | 0.48% | 8am–11am, Tue | UA 2412 08:30 |
| 2. IAD → DENWashington to Denver | United Airlines | 83.7% | 84.1% | 0.50% | 5am–8am, Tue | UA 1587 12:48 |
| 3. IAD → DENWashington to Denver | Southwest Airlines | 77.6% | 78.4% | 1.01% | 5am–8am, Sat | — |
| 4. DCA → DENWashington to Denver | Frontier Airlines | 77.3% | 78.1% | 1.02% | 11am–2pm, Sat | F9 685 07:00 |
| 5. BWI → DENBaltimore to Denver | Southwest Airlines | 70.9% | 72.2% | 1.82% | 5am–8am, 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 25 points, against 6 points between the best and worst carrier.
- 5am–8am354 flights93.4%
- 8am–11am758 flights89.4%
- 11am–2pm391 flights90.5%
- 2pm–5pm818 flights79.9%
- 5pm–8pm620 flights68.4%
- 8pm–5am446 flights83.9%
Scale runs 60% to 100%.
Book the early departure. Flights leaving between 5am–8am arrive on time 93.4% of the time, against 68.4% for the evening window. That is 25 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 818 flights scheduled in it.
Explore
Filter IAD to DEN 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 IAD to DEN, the best departure window is 5am–8am at 93.4% on time and the worst is 5pm–8pm at 68.4%, a wide gap of 25.0 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am93.4%
- 8–11am89.4%
- 11am–2pm90.5%
- 2–5pm79.9%
- 5–8pm68.4%
- 8pm–5am83.9%
best all US flightsScale 60% to 100%.
Across the year
When delays peak on this route
This route's year swings by 16 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.
August is the worst month at 75.0% on time, 16 points below November, the best at 91.3%. 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, Tuesday is the strongest day at 86.5% on time and Thursday the weakest at 78.8%, a spread of 8 points.
Delay causes
Why this route gets delayed
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 36,000 reported delay minutes.
- 35%Late-arriving aircraft
- 34%National Airspace System
- 24%Carrier
- 7%Extreme weather
- 0%Security
35% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 36,000 reported delay minutes here, that single category outweighs weather by 5 to one. The split is drawn from 35,880 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 12,000 minutes out of 36,000, against a national NAS share of 21%.
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
5.5% 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 81.8% on time across 3,385 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 3,387 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 DEN 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. November runs 91.3% on time and August 75.0%, a swing of 16 points. If the dates move at all, move them out of August before you think about anything else. 3,347 completed flights over 12 months sit behind that.
Common questions
IAD to DEN questions
How often is IAD to DEN delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 16.9% of the 3,387 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on IAD to DEN?
United Airlines leads at 84.1% on time across 2,791 flights. Southwest Airlines is at the other end on 78.4%, a gap of 6 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 IAD to DEN?
The 5am–8am departure window is the strongest at 93.4% on time. The 5pm–8pm window is the weakest at 68.4%, 25 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 August delays on IAD to DEN?
August is the weakest month at 75.0% on time, compared with 91.3% in November. Across the year that is 16 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
- DEN to IAD — the return legseparate record
- Washington Dulles International (IAD) delay statistics
- Denver International (DEN) delay statistics
- United Airlines on IAD to DEN84.1%
- Southwest Airlines on IAD to DEN78.4%
- IAD to ATL, a related route78.0%
- PHX to DEN, a related route76.7%
- IAD to SFO, a related route77.5%
- United Airlines on-time record84.1%
- Southwest Airlines on-time record78.4%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. IAD to DEN and DEN to IAD are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Embed IAD to DEN’s on-time badge on your site
Paste this into a web page. The badge shows the current on-time rate, cancellation rate and grade, and updates every month. Preview it, or build a badge for another route or airport.
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.