Route reliability record
DEN→SDF
Denver to Louisville
- Flights
- 1,095
- Period
- September 2025 to August 2026
- Distance
- 1,024 mi
- Carriers
- 2
This route lands a B+, about a point better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 1,095 DEN to SDF flights, of which United Airlines flew 730 at 83.0% on time.
Best time to fly DEN to SDF: a 8am–11am departure, ideally on a Saturday. Flights in that window arrived on time 90.0% of the time and Saturday flights 85.4%, against 78.4% for the route overall.
The US average over the same twelve months is 77.3%, 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
78.4%
Arrivals under 15 minutes late, of 1,086 completed flights
Avg delay
58 min
Across delayed arrivals only, not all flights
Cancelled
0.82%
National rate is 1.89%
Best carrier
United
83.0% on time across 730 flights
These figures cover 1,095 flights between September 2025 and August 2026. The median arrival is 3 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.
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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 83.0% of the time; Southwest Airlines manages 69.0%. Sample sizes sit next to every figure, because a two-point gap across 365 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 730 | 83.0% | 67 min | 0.68% | B+ |
| Southwest Airlines | 365 | 69.0% | 49 min | 1.10% | C |
The spread between United and Southwest is 14 points, wide enough that it should decide the booking. On a hundred trips that is 14 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.
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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 | 82.4% | 83.0% | 0.68% | 8am–11am, Tue | UA 1479 09:45 |
| 2. DEN → SDFDenver to Louisville | Southwest Airlines | 68.2% | 69.0% | 1.10% | 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 18 points, against 14 points between the best and worst carrier.
- 5am–8am1 flights—
- 8am–11am373 flights90.0%
- 11am–2pm170 flights73.5%
- 2pm–5pm70 flights72.5%
- 5pm–8pm467 flights72.2%
- 8pm–5am14 flights—
Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 90.0% of the time, against 72.2% for the evening window. That is 18 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 467 flights scheduled in it.
Explore
Filter DEN to SDF by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On DEN to SDF, the best departure window is 8am–11am at 90.0% on time and the worst is 5pm–8pm at 72.2%, a wide gap of 17.8 points. All US flights leaving 8am–11am ran 83.9%.
- 5–8am—
- 8–11am90.0%
- 11am–2pm73.5%
- 2–5pm72.5%
- 5–8pm72.2%
- 8pm–5am—
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 17 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.
June is the worst month at 70.8% on time, 17 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. May was the busiest month here, with 94 flights.
Across the week, Saturday is the strongest day at 85.4% on time and Thursday the weakest at 71.3%, a spread of 14 points.
Delay causes
Why this route gets delayed
Late-arriving aircraft accounts for 52% of the 14,000 delay minutes carriers reported here, and the remaining four split what is left.
- 52%Late-arriving aircraft
- 31%Carrier
- 16%National Airspace System
- 1%Extreme weather
52% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 14,000 reported delay minutes here, that single category outweighs weather by 52 to one. The split is drawn from 13,724 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 90.0% on time here.
Cancellations are rare at 0.82%, below the national 1.89% 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
6.4% of arrivals land an hour or more late, close to the national 8.3%, so 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.
The return leg is a different operation and performs like one: it runs 84.1% on time across 1,096 flights, 6 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 6 points of difference.
The sample behind these figures is 1,095 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 June 70.8%, a swing of 17 points. If the dates move at all, move them out of June before you think about anything else. 1,086 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 five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 21.6% of the 1,095 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on DEN to SDF?
United Airlines leads at 83.0% on time across 730 flights. Southwest Airlines is at the other end on 69.0%, a gap of 14 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 90.0% on time. The 5pm–8pm window is the weakest at 72.2%, 18 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 June delays on DEN to SDF?
June is the weakest month at 70.8% on time, compared with 88.0% in April. Across the year that is 17 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 SDF83.0%
- Southwest Airlines on DEN to SDF69.0%
- DEN to PHX, a related route75.6%
- ORD to SDF, a related route75.8%
- DEN to SLC, a related route78.2%
- United Airlines on-time record83.0%
- Southwest Airlines on-time record69.0%
- 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.