Route reliability record

ATL→ORD

Atlanta to Chicago

Flights: 6,406
Period: July 2025 to June 2026
Distance: 606 mi
Carriers: 9

This route sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 7 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 6,406 flights, of which United Airlines flew 1,611 at 74.3% on time.

United Airlines is the most reliable of the four carriers covered here at 74.3% on time across 1,611 flights.

On time

70.6%

Arrivals under 15 minutes late, of 6,224 completed flights

Avg delay

81 min

Across delayed arrivals only, not all flights

Cancelled

2.34%

National rate is 1.81%

Best carrier

United

74.3% on time across 1,611 flights

These figures cover 6,406 flights between July 2025 and June 2026. Beyond the headline rate, 11.0% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

Carrier by carrier

Which airline is most reliable on ATL to ORD

The choice of carrier is not cosmetic here. United Airlines arrives on time 74.3% of the time; Frontier Airlines manages 62.8%. Sample sizes sit next to every figure, because a two-point gap across 711 flights means less than a ten-point one.

On-time performance by carrier on ATL to ORD
Airline	Flights	On time	Avg delay	Cancelled	Grade
PSA Airlinesthin sample	5	100.0%	—	0.00%	A+
SkyWest Airlinesthin sample	40	84.2%	88 min	5.00%	B−
Spirit Airlinesthin sample	75	83.8%	38 min	0.00%	B+
United Airlines	1,611	74.3%	92 min	1.55%	C
Republic Airwaysthin sample	287	72.4%	65 min	5.92%	C−
American Airlines	688	72.2%	98 min	3.05%	C−
Envoy Airthin sample	364	71.3%	83 min	2.20%	C
Delta Air Lines	2,625	69.1%	63 min	2.21%	C
Frontier Airlines	711	62.8%	111 min	2.67%	D

American Airlines cancels 3.0% of what it schedules here, the highest in the table. A cancelled flight never appears in an on-time rate, so read that column alongside the punctuality one rather than after it.

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 35 points, against 12 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am786 flights87.1%
8am–11am1,208 flights79.3%
11am–2pm1,126 flights80.2%
2pm–5pm1,124 flights66.8%
5pm–8pm1,137 flights52.5%
8pm–5am1,025 flights60.9%

Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 52.5% on time, against 87.1% 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 8am–11am window is the busiest, with 1,208 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.

Darker means more delays. Figures are on-time percentages.September best, March worst

September is the best month on the calendar at 84.4% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. May was the busiest month here, with 596 flights.

Across the week, Wednesday is the strongest day at 73.9% on time and Monday the weakest at 66.9%. 7 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

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 147,000 reported delay minutes.

National Airspace System
38%
Late-arriving aircraft
29%
Carrier
27%
Extreme weather
6%
Security
0%

38% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 56,000 minutes out of 147,000, against a national NAS share of 21%. The split is drawn from 147,333 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 87.1% on time here.

Cancellations sit at 2.34% against a national 1.81%, which is ordinary. Diversions add another 0.50%.

Connections and stage length

What a delay here actually costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 11.0% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

The 606 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 75.0% on time across 6,409 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 6,406 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 84.4% on time and March 58.5%, a swing of 26 points. If the dates move at all, move them out of March before you think about anything else. 6,224 completed flights over 12 months sit behind that.

Common questions

ATL to ORD questions

How often is ATL to ORD delayed?

Roughly one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 29.4% of the 6,406 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on ATL to ORD?

United Airlines leads at 74.3% on time across 1,611 flights. Frontier Airlines is at the other end on 62.8%, a gap of 12 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 ORD?

The 5am–8am departure window is the strongest at 87.1% on time. The 5pm–8pm window is the weakest at 52.5%, 35 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 March delays on ATL to ORD?

March is the weakest month at 58.5% on time, compared with 84.4% 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.

Where to go next

Direction matters. ATL to ORD and ORD 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.

Key figures