Route reliability record
ATL→ORD
Atlanta to Chicago
- Flights
- 6,390
- Period
- June 2025 to May 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 77.4%. The late ones land a little over an hour behind schedule. That rests on 6,390 flights, of which United Airlines flew 1,575 at 75.7% on time.
United Airlines is the most reliable of the five carriers covered here at 75.7% on time across 1,575 flights.
Key figures
On time
70.5%
Arrivals under 15 minutes late, of 6,216 completed flights
Avg delay
81 min
Across delayed arrivals only, not all flights
Cancelled
2.21%
National rate is 1.80%
Best carrier
United
75.7% on time across 1,575 flights
These figures cover 6,390 flights between June 2025 and May 2026. Beyond the headline rate, 11.1% 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 75.7% of the time; Frontier Airlines manages 61.4%. Sample sizes sit next to every figure, because a two-point gap across 706 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| PSA Airlinesthin sample | 5 | 100.0% | — | 0.00% | A+ |
| SkyWest Airlinesthin sample | 41 | 84.6% | 88 min | 4.88% | B− |
| Spirit Airlinesthin sample | 98 | 82.5% | 40 min | 0.00% | B+ |
| United Airlines | 1,575 | 75.7% | 91 min | 1.40% | B |
| Envoy Air | 387 | 72.8% | 82 min | 2.07% | C |
| Republic Airwaysthin sample | 259 | 72.5% | 65 min | 5.02% | C− |
| American Airlines | 697 | 71.3% | 121 min | 2.73% | C |
| Delta Air Lines | 2,622 | 68.4% | 61 min | 2.14% | C |
| Frontier Airlines | 706 | 61.4% | 104 min | 2.97% | D |
The spread between United and Frontier is 14 points, wide enough that it should decide the booking. On a hundred trips that is 14 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 36 points, against 14 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am771 flights87.2%
- 8am–11am1,281 flights78.9%
- 11am–2pm1,095 flights81.1%
- 2pm–5pm1,155 flights67.0%
- 5pm–8pm1,044 flights51.1%
- 8pm–5am1,044 flights59.8%
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 51.1% on time, against 87.2% 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.
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 84.4% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back.
Across the week, Wednesday is the strongest day at 74.7% on time and Monday the weakest at 66.7%. 8 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 148,000 reported delay minutes.
- 34%National Airspace System
- 30%Late-arriving aircraft
- 29%Carrier
- 7%Extreme weather
- 0%Security
34% 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 50,000 minutes out of 148,000, against a national NAS share of 21%.
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 87.2% on time here.
Cancellations sit at 2.21% against a national 1.80%, which is ordinary. Diversions add another 0.52%.
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. 11.1% of arrivals land a full hour or more behind schedule, against 8.2% 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 74.0% on time across 6,391 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 6,390 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.
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 29.5% of the 6,390 flights in this analysis, against 22.6% 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 75.7% on time across 1,575 flights. Frontier Airlines is at the other end on 61.4%, a gap of 14 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 87.2% on time. The 5pm–8pm window is the weakest at 51.1%, 36 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.
Related
Where to go next
- ORD to ATL — the return legseparate record
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Chicago O'Hare International (ORD) delay statistics
- PSA Airlines on-time record100.0%
- SkyWest Airlines on-time record84.6%
- Spirit Airlines on-time record82.5%
- The best time of day to fly, according to 7.05 million flight records
- Worst months to fly in the US, ranked by the data
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, June 2025 to May 2026. Updated monthly. How this data is collected.