Route reliability record
ATL→MDW
Atlanta to Chicago
- Flights
- 3,527
- Period
- July 2025 to June 2026
- Distance
- 591 mi
- Carriers
- 3
This route lands a B, about a point worse than the national rate of 77.6%. About one flight in four arrive 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 3,527 flights, of which Delta Air Lines flew 1,383 at 81.5% on time.
Delta Air Lines is the most reliable of the three carriers covered here at 81.5% on time across 1,383 flights.
Key figures
On time
76.3%
Arrivals under 15 minutes late, of 3,437 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
1.84%
National rate is 1.81%
Best carrier
Delta
81.5% on time across 1,383 flights
These figures cover 3,527 flights between July 2025 and June 2026. The median arrival is 3 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 ATL to MDW
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 | 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
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 28 points, against 16 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am247 flights92.6%
- 8am–11am693 flights82.6%
- 11am–2pm642 flights85.4%
- 2pm–5pm652 flights75.4%
- 5pm–8pm552 flights66.7%
- 8pm–5am741 flights64.8%
Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 64.8% on time, against 92.6% 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 8pm–5am window is the busiest, with 741 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 26 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.
September is the best month on the calendar at 90.4% 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 324 flights.
Across the week, Wednesday is the strongest day at 82.5% on time and Sunday the weakest at 72.3%. 10 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 47% of the 54,000 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.
- 47%Late-arriving aircraft
- 33%Carrier
- 15%National Airspace System
- 5%Extreme weather
- 0%Security
47% 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 54,000 reported delay minutes here, that single category outweighs weather by 10 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 53,950 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 92.6% on time here.
Cancellations sit at 1.84% against a national 1.81%, which is ordinary. Diversions add another 0.71%.
Connections and stage length
What a delay here actually costs
7.7% 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 are the about an hour kind, 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 is a different operation and performs like one: it runs 79.8% on time across 3,528 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.
The sample behind these figures is 3,527 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 this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 90.4% on time and May 64.4%, a swing of 26 points. If the dates move at all, move them out of May before you think about anything else. 3,437 completed flights over 12 months sit behind that.
Common questions
ATL to MDW questions
How often is ATL to MDW delayed?
About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 23.7% of the 3,527 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on ATL to MDW?
Delta Air Lines leads at 81.5% on time across 1,383 flights. Frontier Airlines is at the other end on 65.2%, a gap of 16 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 ATL to MDW?
The 5am–8am departure window is the strongest at 92.6% on time. The 8pm–5am window is the weakest at 64.8%, 28 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 May delays on ATL to MDW?
May is the weakest month at 64.4% on time, compared with 90.4% in September. Across the year that is 26 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 ATL — the return legseparate record
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Chicago Midway International (MDW) delay statistics
- Delta Air Lines on-time record81.5%
- Southwest Airlines on-time record75.9%
- Frontier Airlines on-time record65.2%
- 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. ATL to MDW and MDW to ATL are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.