Carrier route record
UASTL→DEN
United Airlines · St. Louis to Denver
- Flights
- 1,071
- Period
- July 2025 to June 2026
- Share of route
- 29%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.
United on STL to DEN lands a B+, about a point worse than the national rate of 77.6%. About one flight in four arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 1,071 flights, with a median arrival 3 minutes early.
The US average over the same twelve months is 77.6%, so there is little to separate United on STL to DEN from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
76.6%
Arrivals under 15 minutes late, of 1,059 completed flights
Avg delay
91 min
Across delayed arrivals only, not all flights
Cancelled
0.56%
National rate is 1.81%
Whole route
74.9%
Every carrier on STL to DEN, 3,655 flights
These figures cover 1,071 flights between July 2025 and June 2026. Beyond the headline rate, 9.8% 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.
Carrier by carrier
United against every carrier on STL to DEN
United flew 1,071 of the 3,655 flights on STL to DEN, about 29% of it. Its 76.6% on time is 2 points better than the route as a whole, which runs 74.9%. Ranked by on-time rate it is number two of four carriers on the route, where the range runs from SkyWest at 87.1% to Southwest at 73.3%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
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 |
|---|---|---|---|---|---|
| SkyWest Airlinesthin sample | 142 | 87.1% | 60 min | 0.70% | A+ |
| United Airlines (this page) | 1,071 | 76.6% | 91 min | 0.56% | B+ |
| Frontier Airlinesthin sample | 277 | 74.5% | 83 min | 1.08% | C |
| Southwest Airlines | 2,165 | 73.3% | 60 min | 0.23% | C+ |
Departure window
When United runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 25 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am41 flights90.0%
- 8am–11am364 flights85.0%
- 11am–2pm210 flights79.7%
- 2pm–5pm353 flights64.7%
- 5pm–8pm101 flights76.2%
- 8pm–5am2 flights—
Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 90.0% of the time, against 64.7% for the afternoon window. That is 25 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 364 flights scheduled in it.
Across the year
United on STL to DEN through the year
July is the worst month at 57.8% on time, 33 points below February, the best at 90.4%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. June was the busiest month here, with 120 flights.
Across the week, Friday is the strongest day at 79.7% on time and Monday the weakest at 72.4%. 7 points is a smaller lever than departure hour, but it is free.
Delay causes
Why United runs late on this route
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 22,000 reported delay minutes.
- 34%Late-arriving aircraft
- 34%National Airspace System
- 29%Carrier
- 4%Extreme weather
34% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 22,000 reported delay minutes here, that single category outweighs weather by 10 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 22,446 reported delay minutes.
34% 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 7,537 minutes out of 22,000, against a national NAS share of 21%.
Cancellations are rare at 0.56%, 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 stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.8% 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 770 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 return leg runs 79.5% on time across 1,072 flights, within 3 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
One caution: this is a thin sample. 1,071 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 United on STL to DEN
Put together: treat all of this as provisional. 1,071 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 76.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 1,059 completed flights over 12 months sit behind that.
Related
Where to go next
- STL to DEN, every carrier
- United on DEN to STL, the return leg
- SkyWest Airlines on STL to DEN87.1%
- Frontier Airlines on STL to DEN74.5%
- Southwest Airlines on STL to DEN73.3%
- United Airlines network-wide record
- St. Louis Lambert International (STL) delay statistics
- Denver International (DEN) delay statistics
- Why the first flight of the morning is statistically safest
- How often a connection fails at the major US hubs
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.