Houston, TX · departure reliability

IAH

George Bush Intercontinental

Departures: 119,087
Period: July 2025 to June 2026
Carriers: 11
US rank: #17 by volume

Terminal building and aircraft stands at a US airport

Houston

George Bush Intercontinental lands a B, about a point better than the national rate of 77.6%. About one flight in five arrive 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 119,087 flights, of which Delta Air Lines flew 8,369 at 80.8% on time.

Delta Air Lines is the most reliable of the eleven carriers covered here at 80.8% on time across 8,369 flights.

On time

78.4%

Departures arriving under 15 minutes late at their destination

Avg delay

76 min

Across delayed flights only

Cancelled

1.14%

National rate is 1.81%

Best carrier

Delta

80.8% on time here

These figures cover 119,000 flights between July 2025 and June 2026. Beyond the headline rate, 8.3% 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 airlines run best out of IAH

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 80.8% of the time; JetBlue Airways manages 61.1%. Sample sizes sit next to every figure, because a two-point gap across 542 flights means less than a ten-point one.

On-time performance by carrier departing IAH
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	74,010	79.6%	65 min	0.67%	B+
SkyWest Airlines	14,351	76.8%	92 min	1.16%	B
Delta Air Lines	8,369	80.8%	83 min	1.78%	B
American Airlines	7,752	76.7%	128 min	2.62%	B
Spirit Airlines	5,410	74.7%	74 min	2.81%	C
Frontier Airlines	4,776	70.1%	86 min	1.74%	C
Envoy Air	1,388	77.0%	85 min	2.23%	B
Alaska Airlines	1,205	78.5%	54 min	0.83%	B+
Republic Airways	905	73.7%	76 min	4.20%	C−
JetBlue Airways	542	61.1%	84 min	1.85%	D
PSA Airlines	379	69.0%	131 min	4.22%	C−

PSA Airlines cancels 4.2% 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.

Route by route

Busiest routes out of IAH

Route-level records vary far more than the airport average. These are the 25 busiest departures from IAH, each with its own on-time rate against the airport-wide 78.4%.

Busiest routes from IAH by flight volume
Route	Flights	On time	Avg delay	Cancelled	Grade
IAH to ORD · Chicago	6,080	74.8%	82 min	1.48%	C
IAH to DFW · Dallas-Fort Worth	5,779	75.0%	99 min	2.80%	B
IAH to LAX · Los Angeles	5,260	83.6%	64 min	0.57%	B+
IAH to ATL · Atlanta	4,906	77.5%	67 min	1.92%	B
IAH to DEN · Denver	4,673	81.2%	70 min	0.24%	B+
IAH to LGA · New York	4,053	72.6%	81 min	2.74%	C
IAH to EWR · Newark	3,800	74.6%	71 min	1.89%	C
IAH to MIA · Miami	3,736	77.8%	89 min	1.15%	B
IAH to MCO · Orlando	3,669	81.6%	82 min	1.01%	B
IAH to SFO · San Francisco	3,600	78.6%	66 min	0.47%	B+
IAH to LAS · Las Vegas	3,457	82.4%	72 min	0.81%	B+
IAH to DCA · Washington	3,202	74.8%	73 min	1.81%	C
IAH to MSY · New Orleans	2,962	82.9%	65 min	0.30%	B+
IAH to PHX · Phoenix	2,930	78.7%	86 min	0.82%	B+
IAH to FLL · Fort Lauderdale	2,760	79.8%	66 min	1.20%	B
IAH to AUS · Austin	2,675	79.4%	66 min	0.79%	B+
IAH to SAT · San Antonio	2,411	82.4%	63 min	0.50%	B+
IAH to CLT · Charlotte	2,348	79.5%	104 min	2.04%	B
IAH to DTW · Detroit	2,137	78.8%	73 min	1.22%	B
IAH to SEA · Seattle	2,095	77.5%	54 min	0.53%	B+
IAH to BOS · Boston	2,025	72.6%	73 min	1.23%	C
IAH to SLC · Salt Lake City	1,957	82.6%	79 min	0.51%	B+
IAH to IAD · Washington	1,867	80.4%	59 min	0.43%	B+
IAH to MSP · Minneapolis	1,835	78.6%	86 min	0.98%	B+
IAH to PHL · Philadelphia	1,832	79.7%	117 min	2.07%	B

Departure window

The best time of day to leave IAH

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 18 points, against 20 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am19,625 flights88.7%
8am–11am17,022 flights82.3%
11am–2pm19,336 flights79.4%
2pm–5pm21,097 flights76.2%
5pm–8pm21,770 flights70.4%
8pm–5am20,237 flights74.8%

Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 88.7% of the time, against 70.4% for the evening window. That is 18 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 21,770 flights scheduled in it.

Across the year

When IAH runs late

IAH's year swings by 17 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.January best, July worst

July is the worst month at 68.8% on time, 17 points below January, the best at 85.7%. 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. March was the busiest month here, with 10,492 flights.

Across the week, Tuesday is the strongest day at 82.8% on time and Sunday the weakest at 74.5%. 8 points is a smaller lever than departure hour, but it is free.

Delay causes

Why IAH 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 1.94 million reported delay minutes.

Late-arriving aircraft
37%
Carrier
33%
National Airspace System
23%
Extreme weather
7%
Security
0%

37% 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 1.94 million reported delay minutes here, that single category outweighs weather by 5 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 1,935,654 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 88.7% on time here.

Cancellations sit at 1.14% against a national 1.81%, which is ordinary. Diversions add another 0.26%.

8.3% 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 are the a little over an hour kind, which a normal layover absorbs.

119,087 flights sit behind these numbers, which is a large enough sample that the headline rate is not moving on noise. Where a sub-group falls below 30 flights the site shows a dash instead of a percentage.

What to do with this

Flying out of IAH

Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 85.7% on time and July 68.8%, a swing of 17 points. If the dates move at all, move them out of July before you think about anything else. 117,426 completed flights over 12 months sit behind that.

Common questions

IAH delay questions

How often is Houston (IAH) delayed?

About one flight in five arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 21.6% of the 119,087 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 Houston (IAH)?

Delta Air Lines leads at 80.8% on time across 8,369 flights. JetBlue Airways is at the other end on 61.1%, a gap of 20 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 Houston (IAH)?

The 5am–8am departure window is the strongest at 88.7% on time. The 5pm–8pm window is the weakest at 70.4%, 18 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 Houston (IAH)?

July is the weakest month at 68.8% on time, compared with 85.7% in January. Across the year that is 17 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

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