82% of flights from Washington to Denver arrived on time over the past 12 months. That is better than the typical U.S. route. The 6 a.m. departures ran on time 94% of the time; the 7 p.m. ones 67%. Most reliable airline: United Airlines (83%). 7% of flights arrived more than an hour late or not at all.
How late?
The on-time rate treats a flight 20 minutes late the same as one 5 hours late. Here's the split for IAD → DEN: when a flight was late, it was under 45 minutes late 59% of the time. About 1 in 19 flights landed an hour or more late, and 1 in 106 three hours or more; 0.6% were cancelled outright.
- On time or early82%
- 15–30 min late7.4%
- 30–60 min late4.0%
- 1–2 hours late3.3%
- 2–3 hours late1.1%
- 3+ hours late0.9%
- Diverted0.6%
- Cancelled0.6%
Share of all 3,387 scheduled flights, past 12 months, by arrival time against schedule.
By airline
| Airline | Flights | On time | Cancelled | Typical arrival | 1h+ late | Avg when late | Operated by |
|---|---|---|---|---|---|---|---|
| United Airlines | 2,791 | 83% | 0.5% | −9 min | 5.6% | +68 min | United Airlines |
| Southwest Airlines | 596 | 78% | 1.0% | −1 min | 4.4% | +48 min | Southwest Airlines |
Airline = the name on the ticket. Regional flights (e.g. "Delta Connection") count under the ticketing airline, and the operator is listed.
Best time of day to fly
On-time rate by scheduled departure hour (local time at IAD). Delays build through the day as late planes knock on, so early flights usually do best.
By airline and hour
| Departs | United Airlines | Southwest Airlines |
|---|---|---|
| 5 a.m. | — | 90% |
| 6 a.m. | 95% | — |
| 8 a.m. | 86% | — |
| 9 a.m. | 92% | — |
| 10 a.m. | 89% | — |
| noon | 91% | — |
| 2 p.m. | 81% | — |
| 3 p.m. | 78% | — |
| 4 p.m. | 79% | — |
| 5 p.m. | 69% | 65% |
| 10 p.m. | 85% | — |
Last flight of the day
On IAD → DEN, each airline's last flight of the day was cancelled 0.7% of the time, against 0.6% for its earlier flights, about the same. It arrived 3+ hours late 0.7% of the time (earlier flights: 1.1%). It matters more than the numbers suggest. Miss an earlier flight and there's another one that evening; miss the last one and you're usually waiting until morning.
| Airline | Last departure | Last: cancelled | Last: 3h+ late | Earlier: cancelled | Next morning |
|---|---|---|---|---|---|
| United Airlines | 10:23 p.m. | 0.3% | 0.5% | 0.5% | first flight 6:30 a.m. |
| Southwest Airlines | 4:30 p.m. | 1.2% | 0.8% | 0.9% | first flight 6:20 a.m. |
Last flight = the airline's last scheduled departure on this route that day, on days it flies the route at least twice; past 12 months. Times are typical scheduled times over the latest three months.
By month
Each calendar month pooled over 2023–2026. Best: November (90%). Worst: July (74%).
By day of week
| Day | Flights | On time | Cancelled |
|---|---|---|---|
| Monday | 507 | 84% | 0.4% |
| Tuesday | 460 | 87% | 0.0% |
| Wednesday | 473 | 82% | 0.2% |
| Thursday | 498 | 78% | 0.2% |
| Friday | 503 | 79% | 0.6% |
| Saturday | 452 | 84% | 0.4% |
| Sunday | 494 | 81% | 2.2% |
Why flights were late
Share of delay minutes on flights 15+ minutes late, as reported to BTS by the airlines.
Cancellations: weather 16 · airline 2 · air traffic/airport 2
Month by month
Flight numbers on this route
Regular flights with at least 120 scheduled trips in the past year. Sorted by departure time.
| Flight | Departs | Flights | On time | Cancelled | Typical arrival | Operated by |
|---|---|---|---|---|---|---|
| UA 1865 | 10:13 a.m. | 180 | 89% | 0.0% | −20 min | United Airlines |
| UA 1587 | 12:48 p.m. | 291 | 91% | 0.0% | −12 min | United Airlines |
| UA 1126 | 2:35 p.m. | 124 | 76% | 0.0% | −9 min | United Airlines |
| UA 395 | 3:56 p.m. | 159 | 78% | 0.0% | −8 min | United Airlines |
| UA 599 | 5:41 p.m. | 289 | 68% | 1.0% | +1 min | United Airlines |
| UA 495 | 10:23 p.m. | 310 | 85% | 0.3% | −8 min | United Airlines |
Worst days in the past year
| Date | Flights | On time | Cancelled |
|---|---|---|---|
| Jan 26, 2026 | 9 | 0% | 2 |
| Jan 25, 2026 | 9 | 0% | 9 |
| Feb 17, 2026 | 8 | 25% | 0 |
| Mar 6, 2026 | 10 | 30% | 1 |
| Mar 13, 2026 | 10 | 30% | 0 |
Nearby airport alternatives
Other ways to make the same trip, using airports within 60 miles of Washington or Denver. None has been clearly more reliable than IAD → DEN.
| Route | Flights | On time | Cancelled |
|---|---|---|---|
| IAD → DEN (this route) | 3,387 | 82% | 0.6% |
| DCA → DEN Washington Reagan National to Denver | 1,347 | 77% | 0.9% |
| BWI → DEN Baltimore/Washington to Denver | 2,784 | 74% | 1.4% |
Questions
How often are flights from IAD to DEN on time?
82% of 3,387 scheduled flights from Washington, DC to Denver, CO arrived within 15 minutes of schedule between September 2025 and August 2026. 0.6% were cancelled.
What is the best time of day to fly IAD to DEN?
Flights scheduled to leave at 6 a.m. were the most reliable (94% on time). The 7 p.m. departures were the least (67%).
Which airline is most on time from IAD to DEN?
United Airlines: 83% of its 2,791 flights on the route arrived on time. Southwest Airlines: 78%.
What month has the most delays from IAD to DEN?
July (74% on time). The best month is November (90%), over 2023–2026.
Is the last flight of the day from IAD to DEN more likely to be cancelled?
Not much. Each airline's last IAD–DEN flight of the day was cancelled 0.7% of the time over the past year, against 0.6% for its earlier flights. If the last flight is cancelled, the next one is usually the following morning.
Related
- DEN → IAD (return)
- Washington Dulles (IAD) delays by hour
- Flights into Denver (DEN)
- United Airlines on-time record
- Southwest Airlines on-time record
- Connecting off this flight? Check the risk
Domestic flights by the airlines that report to the U.S. DOT, plus their regional partners. "On time" means arriving less than 15 minutes after schedule; cancelled and diverted flights count as not on time. Past performance is a guide, not a forecast. Method.