Route reliability record
IAH→ORD
Houston to Chicago
- Flights
- 6,063
- 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 6,063 flights, of which United Airlines flew 3,981 at 78.2% on time.
United Airlines is the most reliable of the three carriers covered here at 78.2% on time across 3,981 flights.
Key figures
On time
74.7%
Arrivals under 15 minutes late, of 5,944 completed flights
Avg delay
82 min
Across delayed arrivals only, not all flights
Cancelled
1.45%
National rate is 1.80%
Best carrier
United
78.2% on time across 3,981 flights
These figures cover 6,063 flights between June 2025 and May 2026. Beyond the headline rate, 10.0% 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 IAH to ORD
The choice of carrier is not cosmetic here. United Airlines arrives on time 78.2% of the time; American Airlines manages 67.6%. 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 | 3,981 | 78.2% | 66 min | 0.73% | B+ |
| Envoy Air | 385 | 72.3% | 67 min | 1.04% | C |
| Republic Airwaysthin sample | 339 | 72.1% | 82 min | 2.65% | C |
| American Airlines | 775 | 67.6% | 129 min | 2.97% | C |
| Spirit Airlinesthin sample | 344 | 64.3% | 71 min | 4.65% | D− |
| Frontier Airlinesthin sample | 233 | 61.1% | 135 min | 3.00% | D |
| PSA Airlinesthin sample | 4 | 50.0% | 156 min | 0.00% | F+ |
| SkyWest Airlinesthin sample | 2 | 50.0% | 38 min | 0.00% | F+ |
United leads American by 11 points. Real, but small enough that a better departure time on the weaker carrier can outweigh 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 32 points, against 11 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,422 flights87.4%
- 8am–11am1,066 flights84.1%
- 11am–2pm905 flights73.6%
- 2pm–5pm536 flights71.0%
- 5pm–8pm1,295 flights55.8%
- 8pm–5am839 flights73.8%
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 55.8% on time, against 87.4% 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 19 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 66.5% on time, 19 points below September, the best at 85.8%. 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.
Across the week, Tuesday is the strongest day at 78.6% on time and Sunday the weakest at 69.0%. 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 123,000 reported delay minutes.
- 41%Late-arriving aircraft
- 31%National Airspace System
- 23%Carrier
- 6%Extreme weather
- 0%Security
41% 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 123,000 reported delay minutes here, that single category outweighs weather by 7 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 87.4% on time here.
Cancellations sit at 1.45% against a national 1.80%, which is ordinary. Diversions add another 0.51%.
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. 10.0% 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 6,059 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 6,063 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 85.8% on time and July 66.5%, a swing of 19 points. If the dates move at all, move them out of July before you think about anything else.
Common questions
IAH to ORD questions
How often is IAH to ORD 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 6,063 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 IAH to ORD?
United Airlines leads at 78.2% on time across 3,981 flights. American Airlines is at the other end on 67.6%, a gap of 11 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 IAH to ORD?
The 5am–8am departure window is the strongest at 87.4% on time. The 5pm–8pm window is the weakest at 55.8%, 32 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 IAH to ORD?
July is the weakest month at 66.5% on time, compared with 85.8% in September. Across the year that is 19 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 IAH — the return legseparate record
- George Bush Intercontinental (IAH) delay statistics
- Chicago O'Hare International (ORD) delay statistics
- United Airlines on-time record78.2%
- Envoy Air on-time record72.3%
- Republic Airways on-time record72.1%
- 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. IAH to ORD and ORD to IAH 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.