Carrier route record
WNDEN→STL
Southwest Airlines · Denver to St. Louis
- Flights
- 2,172
- Period
- July 2025 to June 2026
- Share of route
- 59%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on DEN to STL 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 about an hour on average. That is a workable record, not a spotless one. That rests on 2,172 flights, with a median arrival 4 minutes early.
The US average over the same twelve months is 77.6%, so there is little to separate Southwest on DEN to STL from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
76.4%
Arrivals under 15 minutes late, of 2,157 completed flights
Avg delay
58 min
Across delayed arrivals only, not all flights
Cancelled
0.41%
National rate is 1.81%
Whole route
78.1%
Every carrier on DEN to STL, 3,662 flights
These figures cover 2,172 flights between July 2025 and June 2026. The median arrival is 4 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Carrier by carrier
Southwest against every carrier on DEN to STL
Southwest flew 2,172 of the 3,662 flights on DEN to STL, most of the route. Its 76.4% on time is 2 points worse than the route as a whole, which runs 78.1%. Ranked by on-time rate it is last of four carriers on the route, where the range runs from Frontier at 85.9% to Southwest at 76.4%. 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 |
|---|---|---|---|---|---|
| Frontier Airlinesthin sample | 277 | 85.9% | 47 min | 0.36% | A+ |
| United Airlines | 1,072 | 79.5% | 62 min | 0.28% | B+ |
| SkyWest Airlinesthin sample | 141 | 77.0% | 52 min | 0.71% | B+ |
| Southwest Airlines (this page) | 2,172 | 76.4% | 58 min | 0.41% | B+ |
Departure window
When Southwest runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 39 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–8am504 flights93.6%
- 8am–11am429 flights87.3%
- 11am–2pm290 flights79.0%
- 2pm–5pm342 flights69.5%
- 5pm–8pm388 flights54.9%
- 8pm–5am219 flights61.2%
Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 54.9% on time, against 93.6% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 504 flights scheduled in it.
Across the year
Southwest on DEN to STL through the year
August is the worst month at 65.2% on time, 21 points below January, the best at 86.5%. 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. July was the busiest month here, with 211 flights.
Across the week, Tuesday is the strongest day at 82.9% on time and Sunday the weakest at 71.0%. 12 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 59% of the 29,000 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.
- 59%Late-arriving aircraft
- 30%Carrier
- 9%National Airspace System
- 2%Extreme weather
- 1%Security
59% 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 29,000 reported delay minutes here, that single category outweighs weather by 33 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 29,400 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 93.6% on time here.
Cancellations are rare at 0.41%, 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
7.6% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.
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 is a different operation and performs like one: it runs 73.3% on time across 2,165 flights, 3 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 3 points of difference.
The sample behind these figures is 2,172 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
What to do with this
Booking Southwest on DEN to STL
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 86.5% on time and August 65.2%, a swing of 21 points. If the dates move at all, move them out of August before you think about anything else. 2,157 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to STL, every carrier
- Southwest on STL to DEN, the return leg
- Frontier Airlines on DEN to STL85.9%
- United Airlines on DEN to STL79.5%
- SkyWest Airlines on DEN to STL77.0%
- Southwest Airlines network-wide record
- Denver International (DEN) delay statistics
- St. Louis Lambert International (STL) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.