Flight number record
UA 599
United Airlines · Washington to Denver
- Route
- IAD → DEN
- Departs
- 17:41
- Flights
- 289
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 599, check with United Airlines.
UA 599 sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 8 points worse than the national rate of 77.3%. The late ones land a little over an hour behind schedule. That rests on 289 flights, with a median arrival 1 minute late.
The national on-time rate over the same period is 77.3%, so UA 599 runs 8 points behind the country as a whole. Across a thousand flights that is about 79 extra late arrivals.
Key figures
On time
69.4%
Arrivals under 15 minutes late, of 284 completed flights
Avg delay
77 min
Across delayed arrivals only, not all flights
Cancelled
1.04%
National rate is 1.89%
1 hour+ late
13.4%
National rate is 8.3%
These figures cover 289 flights between September 2025 and August 2026. Beyond the headline rate, 13.4% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Schedule
When UA 599 flies
UA 599 flies IAD to DEN without a single fixed slot. Its most common scheduled departure was 17:41, used on 82 of 289 flights, with 17:20 (68 flights) and 17:15 (41 flights) next.
- Departs 17:4182 flights28.4%
- Departs 17:2068 flights23.5%
- Departs 17:1541 flights14.2%
Scale runs 0% to 100%.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 17:41 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.0%, and UA 599 runs level with that at 69.4%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.
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Against the route
UA 599 next to IAD to DEN
Every carrier on IAD to DEN combined arrived on time 83.1% of the time across 3,387 flights, so UA 599 is 14 points behind it. United flew 2,791 flights on the same city pair under all its flight numbers, including this one, and those ran 84.1% on time. Across its whole network United Airlines managed 78.8%, which this flight trails by 9 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 599thin sample | 289 | 69.4% | 77 min | 1.04% | C |
| All United Airlines on IAD–DEN | 2,791 | 84.1% | 68 min | 0.50% | B+ |
| All carriers on IAD–DEN | 3,387 | 83.1% | 63 min | 0.59% | B+ |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 599 quarter by quarter
UA 599 did not run the same all year. Its best quarter was Oct–Dec 2025 at 76.1% on time and its weakest Jul–Sep 2026 at 51.7%, a swing of 24 points on roughly 72 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
- Oct–Dec 202567 flights76.1%
- Jan–Mar 202669 flights72.1%
- Apr–Jun 202691 flights73.6%
- Jul–Sep 202662 flights51.7%
Scale runs 45% to 80%.
By weekday, UA 599 did best on Tuesday at 78.0% on time and worst on Friday at 55.0%. Each day rests on about 41 flights, so a gap of 23 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 599 runs when it is late
The 87 late arrivals split 33 under half an hour, 16 between 30 and 60 minutes, and 38 an hour or more.
- 15+ min early51 flights18.0%
- Within 15 min146 flights51.4%
- 15–29 min late33 flights11.6%
- 30–59 min late16 flights5.6%
- 1–2 hours late20 flights7.0%
- 2+ hours late18 flights6.3%
Scale runs 0% to 100%.
Share of 284 completed flights by arrival against schedule.
21 of 78 late departures made up the time and arrived on time, 27% of them. In the other direction, 30 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 UA 599
The latest arrival of the period was on 12 June 2026, 8 hours 45 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 |
|---|---|---|
| 12 June 2026 | 8 hours 45 minutes | Late-arriving aircraft |
| 3 May 2026 | 5 hours 8 minutes | Late-arriving aircraft |
| 10 August 2026 | 4 hours 33 minutes | Late-arriving aircraft |
| 15 March 2026 | 4 hours 16 minutes | Extreme weather |
| 26 December 2025 | 4 hours 8 minutes | Late-arriving aircraft |
Delay causes
Why UA 599 runs late
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 6,720 reported delay minutes.
- 41%Late-arriving aircraft
- 36%National Airspace System
- 16%Carrier
- 8%Extreme weather
41% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 6,720 reported delay minutes here, that single category outweighs weather by 5 to one. The split is drawn from 6,720 delay minutes reported on UA 599.
Cancellations sit at 1.04% against a national 1.89%, which is ordinary. Diversions add another 0.69%.
Connections and routes
What a delay on this flight costs
13.4% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection here, and two hours if the onward flight is on a separate ticket.
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 same number turns up on four other city pairs in the data, including BNA to IAH (31), DEN to FLL (24) and FLL to IAD (21), but none flew often enough under UA 599 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to IAD to DEN only.
One caution: this is a thin sample. 289 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 UA 599
For a booking, UA 599 is a flight to put a long connection behind. 13.4% of its completed flights arrived an hour or more late, which a short layover will not absorb. If the onward flight is on a separate ticket, the risk sits with you.
Related
Where to go next
- IAD to DEN, every carrier and departure
- DEN to IAD, the return direction
- United Airlines 495 on the same route85.4%
- United Airlines 1587 on the same route91.7%
- Washington Dulles International (IAD) delay statistics
- Denver International (DEN) delay statistics
- United Airlines on-time record
- Every United Airlines flight number with a record
- The most and least reliable flight numbers in the US
- Why the first flight of the morning is statistically safest
A flight number here means United Airlines’s own number as it reports to the DOT. How the figures are computed is on the methodology page.
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.