Route reliability record
SDF→DEN
Louisville to Denver
- Flights
- 1,096
- Period
- September 2025 to August 2026
- Distance
- 1,024 mi
- Carriers
- 2
This route earns a B. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.3%. When something does go wrong the average delay runs about an hour. That rests on 1,096 SDF to DEN flights, of which United Airlines flew 730 at 85.8% on time.
Best time to fly SDF to DEN: a 5am–8am departure, ideally on a Saturday. Flights in that window arrived on time 95.5% of the time and Saturday flights 87.4%, against 84.1% for the route overall.
Set against the rest of the country, this route's record is 7 points better than the US average of 77.3%. That gap is worth roughly 68 fewer late arrivals for every thousand flights.
Key figures
On time
84.1%
Arrivals under 15 minutes late, of 1,079 completed flights
Avg delay
65 min
Across delayed arrivals only, not all flights
Cancelled
1.00%
National rate is 1.89%
Best carrier
United
85.8% on time across 730 flights
These figures cover 1,096 flights between September 2025 and August 2026. The median arrival is 8 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 SDF to DEN
The two carriers here are closely matched: 5 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 730 | 85.8% | 72 min | 0.96% | A+ |
| Southwest Airlines | 366 | 80.6% | 55 min | 1.09% | B |
No carrier stands out. United tops the table at 85.8%, 5 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Flights on SDF to DEN
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 Louisville to Denver
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. SDF → DENLouisville to Denver | United Airlines | 85.0% | 85.8% | 0.96% | 8am–11am, Sat | UA 1510 15:25 |
| 2. SDF → DENLouisville to Denver | Southwest Airlines | 79.7% | 80.6% | 1.09% | 5am–8am, Wed | — |
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 25 points, against 5 points between the best and worst carrier.
- 5am–8am90 flights95.5%
- 8am–11am377 flights91.2%
- 11am–2pm159 flights79.0%
- 2pm–5pm419 flights78.7%
- 5pm–8pm51 flights70.6%
- 8pm–5am—
Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 95.5% of the time, against 70.6% for the evening 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 2pm–5pm window is the busiest, with 419 flights scheduled in it.
Explore
Filter SDF to DEN 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 SDF to DEN, the best departure window is 5am–8am at 95.5% on time and the worst is 5pm–8pm at 70.6%, a wide gap of 24.9 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am95.5%
- 8–11am91.2%
- 11am–2pm79.0%
- 2–5pm78.7%
- 5–8pm70.6%
- 8pm–5am—
best all US flightsScale 60% to 100%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 23 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.
December is the weak month at 69.6% on time, against 92.2% in September. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. May was the busiest month here, with 95 flights.
Across the week, Saturday is the strongest day at 87.4% on time and Monday the weakest at 82.1%, a spread of 5 points.
Delay causes
Why this route gets delayed
Carrier accounts for 46% of the 11,000 delay minutes carriers reported here, and the remaining four split what is left.
- 46%Carrier
- 26%National Airspace System
- 25%Late-arriving aircraft
- 3%Extreme weather
The largest share of delay minutes, 46%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 5,161 of the 11,000 delay minutes reported here. The split is drawn from 11,245 reported delay minutes.
Cancellations sit at 1.00% against a national 1.89%, which is ordinary. Diversions add another 0.55%.
Connections and stage length
What a delay here actually costs
5.6% 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 78.4% on time across 1,095 flights, 6 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 6 points of difference.
The sample behind these figures is 1,096 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 DEN 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. September runs 92.2% on time and December 69.6%, a swing of 23 points. If the dates move at all, move them out of December before you think about anything else. 1,079 completed flights over 12 months sit behind that.
Common questions
SDF to DEN questions
How often is SDF to DEN delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 15.9% of the 1,096 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SDF to DEN?
United Airlines leads at 85.8% on time across 730 flights. Southwest Airlines is at the other end on 80.6%, a gap of 5 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 SDF to DEN?
The 5am–8am departure window is the strongest at 95.5% on time. The 5pm–8pm window is the weakest at 70.6%, 25 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 December delays on SDF to DEN?
December is the weakest month at 69.6% on time, compared with 92.2% in September. Across the year that is 23 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
- DEN to SDF — the return legseparate record
- Denver International (DEN) delay statistics
- United Airlines on SDF to DEN85.8%
- Southwest Airlines on SDF to DEN80.6%
- SDF to ORD, a related route79.3%
- PHX to DEN, a related route76.7%
- SDF to ATL, a related route89.6%
- United Airlines on-time record85.8%
- Southwest Airlines on-time record80.6%
- The best time of day to fly, according to 7.05 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. SDF to DEN and DEN to SDF 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.