Route reliability record
DEN→SDF
Denver to Louisville
- Flights
- 1,102
- Period
- July 2025 to June 2026
- Distance
- 1,024 mi
- Carriers
- 2
This route 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 77.6%. The late ones land about an hour behind schedule. That rests on 1,102 DEN to SDF flights, of which United Airlines flew 731 at 80.9% on time.
Best time to fly DEN to SDF: a 8am–11am departure, ideally on a Saturday. Flights in that window arrived on time 88.8% of the time and Saturday flights 82.4%, against 75.8% for the route overall.
The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
75.8%
Arrivals under 15 minutes late, of 1,093 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
0.82%
National rate is 1.81%
Best carrier
United
80.9% on time across 731 flights
These figures cover 1,102 flights between July 2025 and June 2026. The median arrival is 2 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
Which airline is most reliable on DEN to SDF
The choice of carrier is not cosmetic here. United Airlines arrives on time 80.9% of the time; Southwest Airlines manages 65.8%. Sample sizes sit next to every figure, because a two-point gap across 371 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 731 | 80.9% | 63 min | 0.55% | B+ |
| Southwest Airlines | 371 | 65.8% | 61 min | 1.35% | C |
The spread between United and Southwest is 15 points, wide enough that it should decide the booking. On a hundred trips that is 15 more arrivals inside the on-time window.
Flight by flight
Flights on DEN to SDF
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
Best ways to make this trip
The most reliable ways to fly Denver to Louisville
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. DEN → SDFDenver to Louisville | United Airlines | 80.5% | 80.9% | 0.55% | 8am–11am, Tue | UA 1479 09:45 |
| 2. DEN → SDFDenver to Louisville | Southwest Airlines | 64.9% | 65.8% | 1.35% | 11am–2pm, Sat | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 37 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1 flights—
- 8am–11am378 flights88.8%
- 11am–2pm135 flights76.3%
- 2pm–5pm75 flights71.6%
- 5pm–8pm477 flights68.0%
- 8pm–5am36 flights51.4%
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 51.4% on time, against 88.8% for the 8am–11am 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 5pm–8pm window is the busiest, with 477 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 36 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
July is the worst month at 52.1% on time, 36 points below April, the best at 88.0%. 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 97 flights.
Across the week, Saturday is the strongest day at 82.4% on time and Thursday the weakest at 67.5%. 15 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Late-arriving aircraft accounts for 58% of the 16,000 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.
- 58%Late-arriving aircraft
- 26%Carrier
- 14%National Airspace System
- 2%Extreme weather
58% 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 16,000 reported delay minutes here, that single category outweighs weather by 38 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 16,363 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 88.8% on time here.
Cancellations are rare at 0.82%, 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 actually costs
7.7% 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 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 83.0% on time across 1,103 flights, 7 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 7 points of difference.
The sample behind these figures is 1,102 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.
Work out the risk of missing a connection in SDF after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 88.0% on time and July 52.1%, a swing of 36 points. If the dates move at all, move them out of July before you think about anything else. 1,093 completed flights over 12 months sit behind that.
Common questions
DEN to SDF questions
How often is DEN to SDF delayed?
About one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 24.2% of the 1,102 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on DEN to SDF?
United Airlines leads at 80.9% on time across 731 flights. Southwest Airlines is at the other end on 65.8%, a gap of 15 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on DEN to SDF?
The 8am–11am departure window is the strongest at 88.8% on time. The 8pm–5am window is the weakest at 51.4%, 37 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are July delays on DEN to SDF?
July is the weakest month at 52.1% on time, compared with 88.0% in April. Across the year that is 36 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- SDF to DEN — the return legseparate record
- Denver International (DEN) delay statistics
- United Airlines on DEN to SDF80.9%
- Southwest Airlines on DEN to SDF65.8%
- DEN to PHX, a related route75.7%
- ORD to SDF, a related route75.3%
- DEN to SLC, a related route77.5%
- United Airlines on-time record80.9%
- Southwest Airlines on-time record65.8%
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
Direction matters. DEN to SDF and SDF to DEN are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.