Route reliability record
MDW→STL
Chicago to St. Louis
- Flights
- 1,705
- Period
- July 2025 to June 2026
- Distance
- 251 mi
- Carriers
- 1
This route lands a B, 4 points better than the national rate of 77.6%. Roughly 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 1,705 MDW to STL flights, with a median arrival 9 minutes early.
Best time to fly MDW to STL: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 96.3% of the time and Tuesday flights 86.6%, against 81.6% for the route overall.
Set against the rest of the country, this route's record is 4 points better than the US average of 77.6%. That gap is worth roughly 40 fewer late arrivals for every thousand flights.
Key figures
On time
81.6%
Arrivals under 15 minutes late, of 1,686 completed flights
Avg delay
60 min
Across delayed arrivals only, not all flights
Cancelled
1.06%
National rate is 1.81%
Best carrier
Southwest
81.6% on time across 1,705 flights
These figures cover 1,705 flights between July 2025 and June 2026. The median arrival is 9 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 STL
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 | 1,705 | 81.6% | 60 min | 1.06% | B |
Best ways to make this trip
The most reliable ways to fly Chicago to St. Louis
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. 4 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. MDW → STLChicago to St. Louis | Southwest Airlines | 80.7% | 81.6% | 1.06% | 5am–8am, Tue | — |
| 2. ORD → STLChicago to St. Louis | Republic Airways | 74.3% | 76.2% | 2.48% | 11am–2pm, Sat | — |
| 3. ORD → STLChicago to St. Louis | Envoy Air | 73.2% | 75.0% | 2.34% | 5am–8am, Tue | — |
| 4. ORD → STLChicago to St. Louis | United Airlines | 70.3% | 71.2% | 1.33% | 11am–2pm, Thu | — |
| 5. ORD → STLChicago to St. Louis | SkyWest Airlines | 65.3% | 68.2% | 4.20% | 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 half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am272 flights96.3%
- 8am–11am344 flights92.0%
- 11am–2pm258 flights84.6%
- 2pm–5pm280 flights77.3%
- 5pm–8pm299 flights68.9%
- 8pm–5am252 flights67.7%
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 96.3% of the time, against 67.7% for the overnight 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 8am–11am window is the busiest, with 344 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 21 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 71.3% on time, 21 points below September, the best at 92.7%. 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 169 flights.
Across the week, Tuesday is the strongest day at 86.6% on time and Sunday the weakest at 75.9%. 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 54% of the 19,000 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.
- 54%Late-arriving aircraft
- 33%Carrier
- 11%National Airspace System
- 2%Extreme weather
- 0%Security
54% 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 19,000 reported delay minutes here, that single category outweighs weather by 26 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 18,791 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 96.3% on time here.
Cancellations sit at 1.06% against a national 1.81%, which is ordinary. Diversions add another 0.06%.
Connections and stage length
What a delay here actually costs
5.7% 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.
At 251 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 runs 79.7% on time across 1,704 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
The sample behind these figures is 1,705 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 STL 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 92.7% on time and July 71.3%, a swing of 21 points. If the dates move at all, move them out of July before you think about anything else. 1,686 completed flights over 12 months sit behind that.
Common questions
MDW to STL questions
How often is MDW to STL delayed?
Roughly 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 18.4% of the 1,705 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is MDW to STL compared with the rest of the country?
81.6% of flights arrive on time here against a national 77.6%, a difference of 4 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 STL?
The 5am–8am departure window is the strongest at 96.3% on time. The 8pm–5am window is the weakest at 67.7%, 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 July delays on MDW to STL?
July is the weakest month at 71.3% on time, compared with 92.7% in September. Across the year that is 21 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
- STL to MDW — the return legseparate record
- Chicago Midway International (MDW) delay statistics
- St. Louis Lambert International (STL) delay statistics
- MDW to ATL, a related route79.8%
- ATL to STL, a related route82.4%
- MDW to PHX, a related route75.0%
- Southwest Airlines on-time record81.6%
- 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 STL and STL 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.