Route reliability record
ORD→IAH
Chicago to Houston
- Flights
- 6,059
- Period
- June 2025 to May 2026
- Distance
- 925 mi
- Carriers
- 8
This route sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.4%. The late ones land a little over an hour behind schedule. That rests on 6,059 flights, of which United Airlines flew 3,973 at 78.3% on time.
United Airlines is the most reliable of the three carriers covered here at 78.3% on time across 3,973 flights.
Key figures
On time
74.7%
Arrivals under 15 minutes late, of 5,959 completed flights
Avg delay
74 min
Across delayed arrivals only, not all flights
Cancelled
1.40%
National rate is 1.80%
Best carrier
United
78.3% on time across 3,973 flights
These figures cover 6,059 flights between June 2025 and May 2026. Beyond the headline rate, 10.1% 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 ORD to IAH
The choice of carrier is not cosmetic here. United Airlines arrives on time 78.3% of the time; American Airlines manages 61.0%. Sample sizes sit next to every figure, because a two-point gap across 775 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 3,973 | 78.3% | 67 min | 0.73% | B+ |
| Frontier Airlinesthin sample | 234 | 76.2% | 97 min | 2.56% | B |
| Republic Airwaysthin sample | 341 | 75.4% | 68 min | 2.35% | B |
| Envoy Air | 384 | 73.7% | 62 min | 1.30% | C |
| Spirit Airlinesthin sample | 346 | 62.3% | 98 min | 4.91% | D− |
| American Airlines | 775 | 61.0% | 88 min | 2.58% | D |
| PSA Airlinesthin sample | 4 | 50.0% | 74 min | 0.00% | F+ |
| SkyWest Airlinesthin sample | 2 | 0.0% | 32 min | 0.00% | F+ |
The spread between United and American is 17 points, wide enough that it should decide the booking. On a hundred trips that is 17 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 23 points, against 17 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,084 flights86.8%
- 8am–11am1,161 flights82.2%
- 11am–2pm670 flights80.3%
- 2pm–5pm1,272 flights68.0%
- 5pm–8pm790 flights67.7%
- 8pm–5am1,082 flights63.5%
Scale runs 55% to 90%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 63.5% on time, against 86.8% 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 22 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.
July is the worst month at 63.6% on time, 22 points below February, the best at 86.1%. 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.
Across the week, Tuesday is the strongest day at 79.7% on time and Sunday the weakest at 69.9%. 10 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 112,000 reported delay minutes.
- 40%Late-arriving aircraft
- 27%Carrier
- 26%National Airspace System
- 7%Extreme weather
- 0%Security
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 112,000 reported delay minutes here, that single category outweighs weather by 6 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 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 86.8% on time here.
Cancellations sit at 1.40% against a national 1.80%, which is ordinary. Diversions add another 0.25%.
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. 10.1% 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 925 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 74.7% on time across 6,063 flights, within half 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 6,059 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. February runs 86.1% on time and July 63.6%, a swing of 22 points. If the dates move at all, move them out of July before you think about anything else.
Common questions
ORD to IAH questions
How often is ORD to IAH 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 25.3% of the 6,059 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 ORD to IAH?
United Airlines leads at 78.3% on time across 3,973 flights. American Airlines is at the other end on 61.0%, a gap of 17 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 ORD to IAH?
The 5am–8am departure window is the strongest at 86.8% on time. The 8pm–5am window is the weakest at 63.5%, 23 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 July delays on ORD to IAH?
July is the weakest month at 63.6% on time, compared with 86.1% in February. Across the year that is 22 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
- IAH to ORD — the return legseparate record
- Chicago O'Hare International (ORD) delay statistics
- George Bush Intercontinental (IAH) delay statistics
- United Airlines on-time record78.3%
- Frontier Airlines on-time record76.2%
- Republic Airways on-time record75.4%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. ORD to IAH and IAH to ORD 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.