Route reliability record
ATL→IAH
Atlanta to Houston
- Flights
- 4,908
- Period
- June 2025 to May 2026
- Distance
- 689 mi
- Carriers
- 4
This route sits in the middle of the pack with a B. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.4%. The late ones land a little over an hour behind schedule. That rests on 4,908 flights, of which United Airlines flew 1,234 at 84.9% on time.
United Airlines is the most reliable of the four carriers covered here at 84.9% on time across 1,234 flights.
Key figures
On time
75.4%
Arrivals under 15 minutes late, of 4,801 completed flights
Avg delay
71 min
Across delayed arrivals only, not all flights
Cancelled
2.00%
National rate is 1.80%
Best carrier
United
84.9% on time across 1,234 flights
These figures cover 4,908 flights between June 2025 and May 2026. Beyond the headline rate, 9.9% 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 IAH
The choice of carrier is not cosmetic here. United Airlines arrives on time 84.9% of the time; Spirit Airlines manages 64.1%. Sample sizes sit next to every figure, because a two-point gap across 444 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,234 | 84.9% | 80 min | 1.22% | B |
| Delta Air Lines | 2,492 | 75.9% | 59 min | 2.17% | B |
| Frontier Airlines | 738 | 64.6% | 84 min | 1.22% | D |
| Spirit Airlines | 444 | 64.1% | 82 min | 4.50% | D− |
Spirit Airlines cancels 4.5% 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 17 points, against 21 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am728 flights83.1%
- 8am–11am646 flights81.1%
- 11am–2pm788 flights84.3%
- 2pm–5pm1,115 flights71.9%
- 5pm–8pm569 flights69.1%
- 8pm–5am1,062 flights67.1%
Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 84.3% on time, ahead of 8pm–5am at 67.1%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation.
Across the year
When delays peak on this route
This route's year swings by 28 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.
June is the worst month at 58.2% on time, 28 points below September, the best at 86.2%. 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, Wednesday is the strongest day at 80.4% on time and Monday the weakest at 71.4%. 9 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 83,000 reported delay minutes.
- 37%Carrier
- 34%Late-arriving aircraft
- 26%National Airspace System
- 3%Extreme weather
34% 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 83,000 reported delay minutes here, that single category outweighs weather by 11 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 largest share of delay minutes, 37%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 30,000 of the 83,000 delay minutes reported here.
Cancellations sit at 2.00% against a national 1.80%, which is ordinary. Diversions add another 0.18%.
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. 9.9% 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 689 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 77.1% on time across 4,900 flights, within 2 points 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 4,908 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 86.2% on time and June 58.2%, a swing of 28 points. If the dates move at all, move them out of June before you think about anything else.
Common questions
ATL to IAH questions
How often is ATL 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 24.6% of the 4,908 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 IAH?
United Airlines leads at 84.9% on time across 1,234 flights. Spirit Airlines is at the other end on 64.1%, a gap of 21 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 IAH?
The 11am–2pm departure window is the strongest at 84.3% on time. The 8pm–5am window is the weakest at 67.1%, 17 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 June delays on ATL to IAH?
June is the weakest month at 58.2% on time, compared with 86.2% in September. Across the year that is 28 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 ATL — the return legseparate record
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- George Bush Intercontinental (IAH) delay statistics
- United Airlines on-time record84.9%
- Delta Air Lines on-time record75.9%
- Frontier Airlines on-time record64.6%
- 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. ATL to IAH and IAH 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.