Carrier route record
WNDEN→IAD
Southwest Airlines · Denver to Washington
- Flights
- 595
- Period
- September 2025 to August 2026
- Share of route
- 18%
- Carriers
- 2
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on DEN to IAD draws a C. About one flight in three arrives at least 15 minutes late, and the typical late arrival is roughly 45 minutes behind schedule. Build slack into anything you connect to. That rests on 595 flights, with a median arrival 4 minutes late.
The national on-time rate over the same period is 77.3%, so Southwest on DEN to IAD runs 10 points behind the country as a whole. Across a thousand flights that is about 96 extra late arrivals.
Key figures
On time
67.7%
Arrivals under 15 minutes late, of 589 completed flights
Avg delay
47 min
Across delayed arrivals only, not all flights
Cancelled
1.01%
National rate is 1.89%
Whole route
81.8%
Every carrier on DEN to IAD, 3,385 flights
These figures cover 595 flights between September 2025 and August 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.
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Carrier by carrier
Southwest against every carrier on DEN to IAD
Southwest flew 595 of the 3,385 flights on DEN to IAD, about 18% of it. Its 67.7% on time is 14 points worse than the route as a whole, which runs 81.8%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from United at 84.8% to Southwest at 67.7%.
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 | 2,790 | 84.8% | 66 min | 0.50% | B+ |
| Southwest Airlines (this page) | 595 | 67.7% | 47 min | 1.01% | C |
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Departure window
When Southwest 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–8am27 flights—
- 8am–11am174 flights80.9%
- 11am–2pm90 flights60.0%
- 2pm–5pm90 flights79.5%
- 5pm–8pm213 flights53.8%
- 8pm–5am1 flights—
Scale runs 45% to 85%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 53.8% on time, against 80.9% for the 8am–11am 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 5pm–8pm window is the busiest, with 213 flights scheduled in it.
Across the year
Southwest on DEN to IAD through the year
Delays peak in May, when the on-time rate falls to 50.0%. January is the strongest month at 89.7%. Moving a flexible trip across that boundary buys 40 points. September was the busiest month here, with 82 flights.
Across the week, Tuesday is the strongest day at 76.1% on time and Thursday the weakest at 60.7%, a spread of 15 points.
Arrival by arrival
How late Southwest on DEN to IAD runs when it is late
The 190 late arrivals split 77 under half an hour, 68 between 30 and 60 minutes, and 45 an hour or more.
- 15+ min early55 flights9.3%
- Within 15 min344 flights58.4%
- 15–29 min late77 flights13.1%
- 30–59 min late68 flights11.5%
- 1–2 hours late37 flights6.3%
- 2+ hours late8 flights1.4%
Scale runs 0% to 100%.
Share of 589 completed flights by arrival against schedule.
48 of 202 late departures made up the time and arrived on time, 24% of them. In the other direction, 36 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 IAD.
The worst days
Worst days for Southwest on DEN to IAD
The latest arrival of the period was on 9 September 2025, 5 hours 6 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 9 September 2025 | 5 hours 6 minutes | Late-arriving aircraft |
| 6 March 2026 | 3 hours 25 minutes | Late-arriving aircraft |
| 17 May 2026 | 2 hours 36 minutes | Late-arriving aircraft |
| 22 May 2026 | 2 hours 36 minutes | Carrier |
| 29 December 2025 | 2 hours 35 minutes | Carrier |
Delay causes
Why Southwest runs late on this route
Late-arriving aircraft accounts for 52% of the 8,843 delay minutes carriers reported here, and the remaining four split what is left.
- 52%Late-arriving aircraft
- 31%Carrier
- 16%National Airspace System
- 1%Extreme weather
52% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 8,843 reported delay minutes here, that single category outweighs weather by 52 to one. The split is drawn from 8,843 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 80.9% on time here.
Cancellations sit at 1.01% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
7.6% 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 roughly 45 minutes, 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 is a different operation and performs like one: it runs 78.4% on time across 596 flights, 11 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 11 points of difference.
One caution: this is a thin sample. 595 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Southwest on DEN to IAD
Put together: treat all of this as provisional. 595 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 67.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 589 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to IAD, every carrier
- Southwest on IAD to DEN, the return leg
- United Airlines on DEN to IAD84.8%
- Southwest Airlines network-wide record
- Denver International (DEN) delay statistics
- Washington Dulles International (IAD) 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.