Carrier route record
WNDEN→SDF
Southwest Airlines · Denver to Louisville
- Flights
- 371
- Period
- July 2025 to June 2026
- Share of route
- 34%
- Carriers
- 2
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on DEN to SDF draws a C. About one flight in three arrives at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 371 flights, with a median arrival 5 minutes late.
The national on-time rate over the same period is 77.6%, so Southwest on DEN to SDF runs 12 points behind the country as a whole. Across a thousand flights that is about 118 extra late arrivals.
Key figures
On time
65.8%
Arrivals under 15 minutes late, of 366 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
1.35%
National rate is 1.81%
Whole route
75.8%
Every carrier on DEN to SDF, 1,102 flights
These figures cover 371 flights between July 2025 and June 2026. Beyond the headline rate, 10.9% 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
Southwest against every carrier on DEN to SDF
Southwest flew 371 of the 1,102 flights on DEN to SDF, about 34% of it. Its 65.8% on time is 10 points worse than the route as a whole, which runs 75.8%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from United at 80.9% to Southwest at 65.8%.
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 |
|---|---|---|---|---|---|
| United Airlines | 731 | 80.9% | 63 min | 0.55% | B+ |
| Southwest Airlines (this page) | 371 | 65.8% | 61 min | 1.35% | C |
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 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–8am—
- 8am–11am13 flights—
- 11am–2pm134 flights76.1%
- 2pm–5pm75 flights71.6%
- 5pm–8pm113 flights53.6%
- 8pm–5am36 flights51.4%
Scale runs 45% to 80%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 51.4% on time, against 76.1% for the 11am–2pm 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 11am–2pm window is the busiest, with 134 flights scheduled in it.
Across the year
Southwest on DEN to SDF through the year
July is the worst month at 35.3% on time, 52 points below May, the best at 87.1%. 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 35 flights.
Across the week, Saturday is the strongest day at 80.4% on time and Thursday the weakest at 54.7%. 26 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 67% of the 7,595 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.
- 67%Late-arriving aircraft
- 25%Carrier
- 6%National Airspace System
- 2%Extreme weather
67% 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 7,595 reported delay minutes here, that single category outweighs weather by 27 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 7,595 reported delay minutes.
Cancellations sit at 1.35% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
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. 10.9% 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 1,024 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 79.8% on time across 372 flights, 14 points above 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 14 points of difference.
One caution: this is a thin sample. 371 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 Southwest on DEN to SDF
Put together: treat all of this as provisional. 371 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 65.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 366 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to SDF, every carrier
- Southwest on SDF to DEN, the return leg
- United Airlines on DEN to SDF80.9%
- Southwest Airlines network-wide record
- Denver International (DEN) 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.