Route reliability record
ATL→IAH
Atlanta to Houston
- Flights
- 4,914
- Period
- July 2025 to June 2026
- Distance
- 689 mi
- Carriers
- 4
This route lands a B, about a point worse than the national rate of 77.6%. About one flight in four arrive 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 4,914 flights, of which United Airlines flew 1,255 at 85.1% on time.
United Airlines is the most reliable of the four carriers covered here at 85.1% on time across 1,255 flights.
Key figures
On time
76.4%
Arrivals under 15 minutes late, of 4,816 completed flights
Avg delay
67 min
Across delayed arrivals only, not all flights
Cancelled
1.87%
National rate is 1.81%
Best carrier
United
85.1% on time across 1,255 flights
These figures cover 4,914 flights between July 2025 and June 2026. Beyond the headline rate, 8.8% 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 85.1% of the time; Spirit Airlines manages 66.3%. Sample sizes sit next to every figure, because a two-point gap across 384 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,255 | 85.1% | 78 min | 1.12% | A |
| Delta Air Lines | 2,508 | 75.9% | 55 min | 1.95% | B |
| Frontier Airlines | 767 | 68.9% | 82 min | 1.43% | C |
| Spirit Airlines | 384 | 66.3% | 76 min | 4.69% | C− |
Spirit Airlines cancels 4.7% 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 16 points, against 19 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am749 flights83.2%
- 8am–11am670 flights81.7%
- 11am–2pm757 flights85.4%
- 2pm–5pm1,107 flights71.9%
- 5pm–8pm549 flights72.0%
- 8pm–5am1,082 flights69.2%
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 85.4% on time, ahead of 8pm–5am at 69.2%. 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. The 2pm–5pm window is the busiest, with 1,107 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 21 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 64.9% on time, 21 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. April was the busiest month here, with 469 flights.
Across the week, Wednesday is the strongest day at 80.8% on time and Sunday the weakest at 72.5%. 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 76,000 reported delay minutes.
- 39%Carrier
- 34%Late-arriving aircraft
- 25%National Airspace System
- 3%Extreme weather
The largest share of delay minutes, 39%, 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 29,000 of the 76,000 delay minutes reported here. The split is drawn from 75,693 reported delay minutes.
Cancellations sit at 1.87% against a national 1.81%, which is ordinary. Diversions add another 0.12%.
Connections and stage length
What a delay here actually costs
8.8% 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 about an hour kind, which a normal layover absorbs.
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 77.5% on time across 4,906 flights, within about 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 4,914 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 July 64.9%, a swing of 21 points. If the dates move at all, move them out of July before you think about anything else. 4,816 completed flights over 12 months sit behind that.
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 23.6% of the 4,914 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on ATL to IAH?
United Airlines leads at 85.1% on time across 1,255 flights. Spirit Airlines is at the other end on 66.3%, a gap of 19 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 85.4% on time. The 8pm–5am window is the weakest at 69.2%, 16 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 ATL to IAH?
July is the weakest month at 64.9% on time, compared with 86.2% in September. Across the year that is 21 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 record85.1%
- Delta Air Lines on-time record75.9%
- Frontier Airlines on-time record68.9%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 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, July 2025 to June 2026. Updated monthly. How this data is collected.