Carrier route record
WNATL→MDW
Southwest Airlines · Atlanta to Chicago
- Flights
- 1,545
- Period
- July 2025 to June 2026
- Share of route
- 44%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on ATL to MDW sits in the middle of the pack with a B. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.6%. The late ones land about 55 minutes behind schedule. That rests on 1,545 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 1,383 at 81.5% on time.
The US average over the same twelve months is 77.6%, so there is little to separate Southwest on ATL to MDW from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
75.9%
Arrivals under 15 minutes late, of 1,508 completed flights
Avg delay
55 min
Across delayed arrivals only, not all flights
Cancelled
1.62%
National rate is 1.81%
Whole route
76.3%
Every carrier on ATL to MDW, 3,527 flights
These figures cover 1,545 flights between July 2025 and June 2026. The median arrival is 2 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
Southwest against every carrier on ATL to MDW
Southwest flew 1,545 of the 3,527 flights on ATL to MDW, about 44% of it. Its 75.9% on time is about level with the route as a whole at 76.3%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from Delta at 81.5% to Frontier at 65.2%.
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 81.5% of the time; Frontier Airlines manages 65.2%. Sample sizes sit next to every figure, because a two-point gap across 599 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 1,383 | 81.5% | 58 min | 2.24% | B |
| Southwest Airlines (this page) | 1,545 | 75.9% | 55 min | 1.62% | B |
| Frontier Airlines | 599 | 65.2% | 97 min | 1.50% | C |
The spread between Delta and Frontier is 16 points, wide enough that it should decide the booking. On a hundred trips that is 16 more arrivals inside the on-time window.
Departure window
When Southwest runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 39 points, against 16 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am230 flights92.4%
- 8am–11am221 flights80.6%
- 11am–2pm312 flights85.0%
- 2pm–5pm280 flights71.1%
- 5pm–8pm425 flights64.9%
- 8pm–5am77 flights53.3%
Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 53.3% on time, against 92.4% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5pm–8pm window is the busiest, with 425 flights scheduled in it.
Across the year
Southwest on ATL to MDW through the year
September is the best month on the calendar at 92.0% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. July was the busiest month here, with 146 flights.
Across the week, Wednesday is the strongest day at 84.0% on time and Sunday the weakest at 69.5%. 15 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 51% of the 20,000 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.
- 51%Late-arriving aircraft
- 30%Carrier
- 15%National Airspace System
- 2%Extreme weather
- 1%Security
51% 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 20,000 reported delay minutes here, that single category outweighs weather by 24 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 19,829 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 92.4% on time here.
Cancellations sit at 1.62% against a national 1.81%, which is ordinary. Diversions add another 0.78%.
Connections and stage length
What a delay here 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 55 minutes, which a normal layover absorbs.
The 591 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 runs 76.7% on time across 1,546 flights, within about a point 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 1,545 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.
What to do with this
Booking Southwest on ATL to MDW
Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 92.0% on time and May 53.8%, a swing of 38 points. If the dates move at all, move them out of May before you think about anything else. 1,508 completed flights over 12 months sit behind that.
Related
Where to go next
- ATL to MDW, every carrier
- Southwest on MDW to ATL, the return leg
- Delta Air Lines on ATL to MDW81.5%
- Frontier Airlines on ATL to MDW65.2%
- Southwest Airlines network-wide record
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Chicago Midway International (MDW) delay statistics
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
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.