Route reliability record
SDF→DEN
Louisville to Denver
- Flights
- 1,103
- Period
- July 2025 to June 2026
- Distance
- 1,024 mi
- Carriers
- 2
This route lands a B, 5 points better than the national rate of 77.6%. About one flight in six 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 1,103 SDF to DEN flights, of which United Airlines flew 731 at 84.6% on time.
Best time to fly SDF to DEN: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 96.7% of the time and Wednesday flights 87.7%, against 83.0% for the route overall.
Set against the rest of the country, this route's record is 5 points better than the US average of 77.6%. That gap is worth roughly 54 fewer late arrivals for every thousand flights.
Key figures
On time
83.0%
Arrivals under 15 minutes late, of 1,090 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
1.00%
National rate is 1.81%
Best carrier
United
84.6% on time across 731 flights
These figures cover 1,103 flights between July 2025 and June 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.
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 | 731 | 84.6% | 66 min | 0.96% | B+ |
| Southwest Airlines | 372 | 79.8% | 55 min | 1.08% | B |
No carrier stands out. United tops the table at 84.6%, 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.
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 | 83.8% | 84.6% | 0.96% | 8am–11am, Tue | UA 1510 15:25 |
| 2. SDF → DENLouisville to Denver | Southwest Airlines | 78.9% | 79.8% | 1.08% | 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 29 points, against 5 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am124 flights96.7%
- 8am–11am365 flights91.2%
- 11am–2pm127 flights77.6%
- 2pm–5pm412 flights76.8%
- 5pm–8pm56 flights67.9%
- 8pm–5am19 flights—
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 96.7% of the time, against 67.9% for the evening window. That is 29 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 412 flights scheduled in it.
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. July was the busiest month here, with 97 flights.
Across the week, Wednesday is the strongest day at 87.7% on time and Friday the weakest at 80.0%. 8 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. Carrier accounts for 43% of the 11,000 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.
- 43%Carrier
- 30%National Airspace System
- 24%Late-arriving aircraft
- 3%Extreme weather
The largest share of delay minutes, 43%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 4,922 of the 11,000 delay minutes reported here. The split is drawn from 11,354 reported delay minutes.
Cancellations sit at 1.00% against a national 1.81%, which is ordinary. Diversions add another 0.18%.
Connections and stage length
What a delay here actually costs
5.4% 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 75.8% on time across 1,102 flights, 7 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 7 points of difference.
The sample behind these figures is 1,103 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. 1,090 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 17.0% of the 1,103 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SDF to DEN?
United Airlines leads at 84.6% on time across 731 flights. Southwest Airlines is at the other end on 79.8%, 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 96.7% on time. The 5pm–8pm window is the weakest at 67.9%, 29 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 DEN84.6%
- Southwest Airlines on SDF to DEN79.8%
- SDF to ORD, a related route79.0%
- PHX to DEN, a related route77.2%
- SDF to ATL, a related route90.0%
- United Airlines on-time record84.6%
- Southwest Airlines on-time record79.8%
- The best time of day to fly, according to 7.04 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.
Embed SDF to DEN’s on-time badge on your site
Paste this into a web page. The badge shows the current on-time rate, cancellation rate and grade, and updates every month. Preview it, or build a badge for another route or airport.
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.