Route reliability record
MDW→SDF
Chicago to Louisville
- Flights
- 990
- Period
- July 2025 to June 2026
- Distance
- 271 mi
- Carriers
- 1
This route lands a B, 3 points better than the national rate of 77.6%. About one flight in five 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 990 MDW to SDF flights, with a median arrival 7 minutes early.
Best time to fly MDW to SDF: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 91.1% of the time and Wednesday flights 86.8%, against 80.6% 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
80.6%
Arrivals under 15 minutes late, of 973 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
1.72%
National rate is 1.81%
Best carrier
Southwest
80.6% on time across 990 flights
These figures cover 990 flights between July 2025 and June 2026. The median arrival is 7 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 MDW to SDF
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 |
|---|---|---|---|---|---|
| Southwest Airlines | 990 | 80.6% | 56 min | 1.72% | B |
Best ways to make this trip
The most reliable ways to fly Chicago to Louisville
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 3 of the top 4 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. ORD → SDFChicago to Louisville | Envoy Air | 83.1% | 84.1% | 1.20% | 5am–8am, Tue | — |
| 2. MDW → SDFChicago to Louisville | Southwest Airlines | 79.2% | 80.6% | 1.72% | 5am–8am, Wed | — |
| 3. ORD → SDFChicago to Louisville | Republic Airways | 72.1% | 75.0% | 3.87% | 5am–8am, Thu | YX 3598 17:50 |
| 4. ORD → SDFChicago to Louisville | SkyWest Airlines | 68.8% | 71.0% | 3.10% | 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 23 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–8am92 flights91.1%
- 8am–11am252 flights90.7%
- 11am–2pm129 flights80.5%
- 2pm–5pm148 flights80.3%
- 5pm–8pm180 flights68.4%
- 8pm–5am189 flights73.9%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 91.1% of the time, against 68.4% for the evening window. That is 23 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 252 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 28 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 62.4% on time, 28 points below April, the best at 90.6%. 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 104 flights.
Across the week, Wednesday is the strongest day at 86.8% on time and Monday the weakest at 75.8%. 11 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 59% 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.
- 59%Late-arriving aircraft
- 29%Carrier
- 11%National Airspace System
- 2%Extreme weather
59% 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 11,000 reported delay minutes here, that single category outweighs weather by 37 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 10,579 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 91.1% on time here.
Cancellations sit at 1.72% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here actually costs
6.2% 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.
At 271 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 5am–8am window matters as much as it does.
The return leg is a different operation and performs like one: it runs 84.4% on time across 989 flights, 4 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 4 points of difference.
One caution: this is a thin sample. 990 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.
Work out the risk of missing a connection in SDF after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 990 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 80.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 973 completed flights over 12 months sit behind that.
Common questions
MDW to SDF questions
How often is MDW 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 19.4% of the 990 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is MDW to SDF compared with the rest of the country?
80.6% of flights arrive on time here against a national 77.6%, a difference of 3 points in its favour. That is worth a B on this site's grading scale.
What time of day has the fewest delays on MDW to SDF?
The 5am–8am departure window is the strongest at 91.1% on time. The 5pm–8pm window is the weakest at 68.4%, 23 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 MDW to SDF?
July is the weakest month at 62.4% on time, compared with 90.6% in April. Across the year that is 28 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 MDW — the return legseparate record
- Chicago Midway International (MDW) delay statistics
- MDW to ATL, a related route79.8%
- ORD to SDF, a related route75.3%
- MDW to PHX, a related route75.0%
- Southwest Airlines on-time record80.6%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
Direction matters. MDW to SDF and SDF to MDW 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.