Carrier route record

WNMDW→ATL

Southwest Airlines · Chicago to Atlanta

Flights: 1,546
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 MDW to ATL lands a B, about a point worse than the national rate of 77.6%. About one flight in four 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 1,546 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 1,383 at 86.9% on time.

The US average over the same twelve months is 77.6%, so there is little to separate Southwest on MDW to ATL from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

76.7%

Arrivals under 15 minutes late, of 1,524 completed flights

Avg delay

57 min

Across delayed arrivals only, not all flights

Cancelled

1.29%

National rate is 1.81%

Whole route

79.8%

Every carrier on MDW to ATL, 3,528 flights

These figures cover 1,546 flights between July 2025 and June 2026. The median arrival is 4 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 MDW to ATL

Southwest flew 1,546 of the 3,528 flights on MDW to ATL, about 44% of it. Its 76.7% on time is 3 points worse than the route as a whole, which runs 79.8%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from Delta at 86.9% to Frontier at 71.8%.

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 86.9% of the time; Frontier Airlines manages 71.8%. Sample sizes sit next to every figure, because a two-point gap across 599 flights means less than a ten-point one.

On-time performance by carrier on MDW to ATL
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	1,383	86.9%	93 min	2.53%	A
Southwest Airlines (this page)	1,546	76.7%	57 min	1.29%	B
Frontier Airlines	599	71.8%	52 min	1.67%	C

The spread between Delta and Frontier is 15 points, wide enough that it should decide the booking. On a hundred trips that is 15 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 31 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am182 flights90.6%
8am–11am351 flights88.4%
11am–2pm304 flights76.7%
2pm–5pm313 flights72.8%
5pm–8pm360 flights63.4%
8pm–5am36 flights60.0%

Scale runs 50% to 95%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 60.0% on time, against 90.6% 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 5pm–8pm window is the busiest, with 360 flights scheduled in it.

Across the year

Southwest on MDW to ATL through the year

Darker means more delays. Figures are on-time percentages.January best, June worst

June is the worst month at 63.2% on time, 28 points below January, the best at 90.8%. 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 146 flights.

Across the week, Tuesday is the strongest day at 82.8% on time and Sunday the weakest at 69.5%. 13 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Southwest runs late on this route

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 20,000 reported delay minutes.

Late-arriving aircraft
40%
Carrier
38%
National Airspace System
17%
Extreme weather
4%
Security
2%

40% 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 11 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 20,204 reported delay minutes.

The largest share of delay minutes, 38%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 7,657 of the 20,000 delay minutes reported here.

Cancellations sit at 1.29% against a national 1.81%, which is ordinary. Diversions add another 0.13%.

Connections and stage length

What a delay here costs

6.8% 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 an hour, 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 75.9% on time across 1,545 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 1,546 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 MDW to ATL

Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 90.8% on time and June 63.2%, a swing of 28 points. If the dates move at all, move them out of June before you think about anything else. 1,524 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures