Flight number record
UA 2123
United Airlines · Kansas City to Denver
- Route
- MCI → DEN
- Departs
- 17:15
- Flights
- 273
- Period
- July 2025 to June 2026
Historical statistics for July 2025 to June 2026, not live status. For today’s UA 2123, check with United Airlines.
UA 2123 draws a D+. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is a little over an hour behind schedule. Build slack into anything you connect to. That rests on 273 flights, with a median arrival 6 minutes late.
The national on-time rate over the same period is 77.6%, so UA 2123 runs 16 points behind the country as a whole. Across a thousand flights that is about 161 extra late arrivals.
Key figures
On time
61.5%
Arrivals under 15 minutes late, of 270 completed flights
Avg delay
72 min
Across delayed arrivals only, not all flights
Cancelled
0.37%
National rate is 1.81%
1 hour+ late
15.6%
National rate is 8.1%
These figures cover 273 flights between July 2025 and June 2026. Beyond the headline rate, 15.6% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Schedule
When UA 2123 flies
UA 2123 flies MCI to DEN without a single fixed slot. Its most common scheduled departure was 17:15, used on 80 of 273 flights, with 17:10 (63 flights) and 17:18 (52 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.
- Departs 17:1580 flights29.3%
- Departs 17:1063 flights23.1%
- Departs 17:1852 flights19.0%
Scale runs 0% to 100%. Rows with fewer than 30 flights show a dash.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 17:15 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.2%, and UA 2123 runs 7 points worse at 61.5%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.
Against the route
UA 2123 next to MCI to DEN
Every carrier on MCI to DEN combined arrived on time 76.1% of the time across 4,274 flights, so UA 2123 is 15 points behind it. United flew 1,298 flights on the same city pair under all its flight numbers, including this one, and those ran 77.8% on time. Across its whole network United Airlines managed 79.0%, which this flight trails by 18 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 2123thin sample | 273 | 61.5% | 72 min | 0.37% | D+ |
| All United Airlines on MCI–DEN | 1,298 | 77.8% | 61 min | 0.54% | B+ |
| All carriers on MCI–DEN | 4,274 | 76.1% | 65 min | 0.61% | B+ |
| United Airlines, whole network | 821,041 | 79.0% | 72 min | 1.01% | B |
Across the year
UA 2123 quarter by quarter
UA 2123 did not run the same all year. Its best quarter was Apr–Jun 2026 at 73.2% on time and its weakest Jul–Sep 2025 at 44.4%, a swing of 29 points on roughly 68 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 202592 flights44.4%
- Oct–Dec 202561 flights66.7%
- Jan–Mar 202664 flights70.3%
- Apr–Jun 202656 flights73.2%
Scale runs 35% to 80%. Rows with fewer than 30 flights show a dash.
By weekday, UA 2123 did best on Wednesday at 74.4% on time and worst on Friday at 51.3%. Each day rests on about 39 flights, so a gap of 23 points is worth noticing but could still narrow in another year.
Delay causes
Why UA 2123 runs late
One category carries most of the weight here. National Airspace System accounts for 57% of the 7,439 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 57%National Airspace System
- 24%Late-arriving aircraft
- 11%Carrier
- 8%Extreme weather
57% 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 4,215 minutes out of 7,439, against a national NAS share of 21%. The split is drawn from 7,439 delay minutes reported on UA 2123.
Cancellations are rare at 0.37%, below the national 1.81% 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 routes
What a delay on this flight costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 15.6% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
The 533 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. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The same number turns up on two other city pairs in the data, including DEN to SFO (244) and SJC to DEN (21), but none flew often enough under UA 2123 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to MCI to DEN only.
One caution: this is a thin sample. 273 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 2123
For a booking, UA 2123 is a flight to put a long connection behind. 15.6% 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
- MCI to DEN, every carrier and departure
- DEN to MCI, the return direction
- United Airlines 708 on the same route87.9%
- Frontier Airlines 3375 on the same route76.0%
- Kansas City International (MCI) 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
- How often a connection fails at the major US hubs
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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.