Route reliability record
STL→MDW
St. Louis to Chicago
- Flights
- 1,704
- Period
- July 2025 to June 2026
- Distance
- 251 mi
- Carriers
- 1
This route lands a B, 2 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 55 minutes on average. That is a workable record, not a spotless one. That rests on 1,704 STL to MDW flights, with a median arrival 7 minutes early.
Best time to fly STL to MDW: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 91.1% of the time and Tuesday flights 87.0%, against 79.7% 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
79.7%
Arrivals under 15 minutes late, of 1,682 completed flights
Avg delay
55 min
Across delayed arrivals only, not all flights
Cancelled
1.12%
National rate is 1.81%
Best carrier
Southwest
79.7% on time across 1,704 flights
These figures cover 1,704 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 STL to MDW
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 | 1,704 | 79.7% | 55 min | 1.12% | B |
Best ways to make this trip
The most reliable ways to fly St. Louis to Chicago
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. STL → MDWSt. Louis to Chicago | Southwest Airlines | 78.8% | 79.7% | 1.12% | 5am–8am, Tue | — |
| 2. STL → ORDSt. Louis to Chicago | American Airlines | 78.7% | 80.7% | 2.44% | 5am–8am, Wed | — |
| 3. STL → ORDSt. Louis to Chicago | Envoy Air | 72.7% | 74.6% | 2.61% | 5am–8am, Sat | — |
| 4. STL → ORDSt. Louis to Chicago | Republic Airways | 69.1% | 72.0% | 4.02% | 5am–8am, Sat | — |
| 5. STL → ORDSt. Louis to Chicago | United Airlines | 67.6% | 68.6% | 1.52% | 11am–2pm, Mon | — |
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 22 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–8am421 flights91.1%
- 8am–11am243 flights88.7%
- 11am–2pm208 flights82.3%
- 2pm–5pm375 flights72.2%
- 5pm–8pm241 flights68.9%
- 8pm–5am216 flights70.2%
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 68.9% for the evening window. That is 22 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 421 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 22 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 68.3% on time, 22 points below November, the best at 90.2%. 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 87.0% on time and Thursday the weakest at 73.4%. 14 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 49% of the 18,000 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.
- 49%Late-arriving aircraft
- 26%Carrier
- 21%National Airspace System
- 4%Extreme weather
- 0%Security
49% 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 18,000 reported delay minutes here, that single category outweighs weather by 13 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 18,454 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 1.12% against a national 1.81%, which is ordinary. Diversions add another 0.18%.
Connections and stage length
What a delay here actually costs
5.8% 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 55 minutes, 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 81.6% on time across 1,705 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 1,704 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 MDW 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. November runs 90.2% on time and July 68.3%, a swing of 22 points. If the dates move at all, move them out of July before you think about anything else. 1,682 completed flights over 12 months sit behind that.
Common questions
STL to MDW questions
How often is STL to MDW 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 20.3% of the 1,704 flights in this analysis, against 22.4% nationally. Delayed flights are late by about 55 minutes on average.
How reliable is STL to MDW compared with the rest of the country?
79.7% of flights arrive on time here against a national 77.6%, a difference of 2 points in its favour. That is worth a B on this site's grading scale.
What time of day has the fewest delays on STL to MDW?
The 5am–8am departure window is the strongest at 91.1% on time. The 5pm–8pm window is the weakest at 68.9%, 22 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 STL to MDW?
July is the weakest month at 68.3% on time, compared with 90.2% in November. Across the year that is 22 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
- MDW to STL — the return legseparate record
- St. Louis Lambert International (STL) delay statistics
- Chicago Midway International (MDW) delay statistics
- STL to ATL, a related route85.3%
- ATL to MDW, a related route76.3%
- STL to DEN, a related route74.9%
- Southwest Airlines on-time record79.7%
- 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. STL to MDW and MDW to STL 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.