Flight number record
UA 645
United Airlines · Denver to Sioux Falls
- Route
- DEN → FSD
- Departs
- 17:28
- Flights
- 338
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 645, check with United Airlines.
UA 645 sits in the middle of the pack with a B. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.3%. The late ones land an hour and a half behind schedule. That rests on 338 flights, with a median arrival 4 minutes early.
Key figures
On time
75.8%
Arrivals under 15 minutes late, of 331 completed flights
Avg delay
88 min
Across delayed arrivals only, not all flights
Cancelled
1.18%
National rate is 1.89%
1 hour+ late
10.3%
National rate is 8.3%
These figures cover 338 flights between September 2025 and August 2026. Beyond the headline rate, 10.3% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Schedule
When UA 645 flies
UA 645 flies DEN to FSD without a single fixed slot. Its most common scheduled departure was 17:28, used on 81 of 338 flights, with 17:50 (59 flights) and 17:42 (37 flights) next.
- Departs 17:2881 flights24.0%
- Departs 17:5059 flights17.5%
- Departs 17:4237 flights10.9%
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 17:28 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.0%, and UA 645 runs 8 points better at 75.8%. 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 645 next to DEN to FSD
Every carrier on DEN to FSD combined arrived on time 82.8% of the time across 1,817 flights, so UA 645 is 7 points behind it. Across its whole network United Airlines managed 78.8%, which this flight trails by 3 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 645thin sample | 338 | 75.8% | 88 min | 1.18% | B |
| All United Airlines on DEN–FSD | 365 | 75.9% | 86 min | 1.10% | B |
| All carriers on DEN–FSD | 1,817 | 82.8% | 80 min | 0.94% | B+ |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 645 quarter by quarter
UA 645 did not run the same all year. Its best quarter was Oct–Dec 2025 at 79.1% on time and its weakest Jul–Sep 2026 at 65.5%, a swing of 14 points on roughly 85 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.
- Jul–Sep 20256 flights—
- Oct–Dec 202591 flights79.1%
- Jan–Mar 202690 flights77.0%
- Apr–Jun 202690 flights78.7%
- Jul–Sep 202661 flights65.5%
Scale runs 55% to 85%. Rows with fewer than 30 flights show a dash.
By weekday, UA 645 did best on Tuesday at 85.4% on time and worst on Thursday at 64.6%. Each day rests on about 48 flights, so a gap of 21 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 645 runs when it is late
The 80 late arrivals split 22 under half an hour, 24 between 30 and 60 minutes, and 34 an hour or more.
- 15+ min early65 flights19.6%
- Within 15 min186 flights56.2%
- 15–29 min late22 flights6.6%
- 30–59 min late24 flights7.3%
- 1–2 hours late15 flights4.5%
- 2+ hours late19 flights5.7%
Scale runs 0% to 100%.
Share of 331 completed flights by arrival against schedule.
14 of 82 late departures made up the time and arrived on time, 17% of them. 12 flights left on time and still arrived late.
The worst days
Worst days for UA 645
The latest arrival of the period was on 26 September 2025, 6 hours 47 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 |
|---|---|---|
| 26 September 2025 | 6 hours 47 minutes | Late-arriving aircraft |
| 8 June 2026 | 5 hours 35 minutes | Late-arriving aircraft |
| 13 August 2026 | 5 hours 8 minutes | Late-arriving aircraft |
| 20 May 2026 | 5 hours 7 minutes | Late-arriving aircraft |
| 8 July 2026 | 4 hours 49 minutes | Carrier |
Delay causes
Why UA 645 runs late
Late-arriving aircraft accounts for 64% of the 7,057 delay minutes carriers reported here, and the remaining four split what is left.
- 64%Late-arriving aircraft
- 26%Carrier
- 9%National Airspace System
- 1%Extreme weather
64% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 7,057 reported delay minutes here, that single category outweighs weather by 47 to one. The split is drawn from 7,057 delay minutes reported on UA 645.
Cancellations sit at 1.18% against a national 1.89%, which is ordinary. Diversions add another 0.89%.
Connections and routes
What a delay on this flight costs
10.3% 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 same number turns up on four other city pairs in the data, including TPA to DEN (180), MCI to DEN (24) and DEN to BOS (24), but none flew often enough under UA 645 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to DEN to FSD only.
One caution: this is a thin sample. 338 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 645
For a booking, UA 645 is one of the weaker ways to fly DEN to FSD: 7 points below the route as a whole. If the schedule allows, compare it with the other departures listed on the route page before settling on this one.
Related
Where to go next
- DEN to FSD, every carrier and departure
- FSD to DEN, the return direction
- SkyWest Airlines 4759 on the same route88.9%
- SkyWest Airlines 5378 on the same route86.4%
- SkyWest Airlines 5700 on the same route80.5%
- 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.