Route reliability record
IAH→ATL
Houston to Atlanta
- Flights
- 4,900
- Period
- June 2025 to May 2026
- Distance
- 689 mi
- Carriers
- 4
This route lands a B, level with the national rate of 77.4%. Roughly one flight in four 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 4,900 flights, of which United Airlines flew 1,236 at 81.9% on time.
United Airlines is the most reliable of the four carriers covered here at 81.9% on time across 1,236 flights.
Key figures
On time
77.1%
Arrivals under 15 minutes late, of 4,799 completed flights
Avg delay
71 min
Across delayed arrivals only, not all flights
Cancelled
2.02%
National rate is 1.80%
Best carrier
United
81.9% on time across 1,236 flights
These figures cover 4,900 flights between June 2025 and May 2026. Beyond the headline rate, 8.5% 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 ATL
The choice of carrier is not cosmetic here. United Airlines arrives on time 81.9% of the time; Frontier Airlines manages 60.3%. Sample sizes sit next to every figure, because a two-point gap across 738 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,236 | 81.9% | 71 min | 0.81% | B+ |
| Delta Air Lines | 2,491 | 79.9% | 75 min | 2.29% | B |
| Spirit Airlines | 435 | 75.4% | 55 min | 3.68% | B− |
| Frontier Airlines | 738 | 60.3% | 71 min | 2.17% | D |
Spirit Airlines cancels 3.7% 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 22 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,561 flights83.2%
- 8am–11am443 flights80.5%
- 11am–2pm870 flights79.8%
- 2pm–5pm813 flights72.6%
- 5pm–8pm888 flights67.5%
- 8pm–5am325 flights72.6%
Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 83.2% of the time, against 67.5% for the evening window. That is 16 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on.
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 63.1% on time, 28 points below September, the best at 91.1%. 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, Wednesday is the strongest day at 83.4% on time and Sunday the weakest at 72.1%. 11 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 78,000 reported delay minutes.
- 41%Late-arriving aircraft
- 33%Carrier
- 23%National Airspace System
- 3%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 78,000 reported delay minutes here, that single category outweighs weather by 12 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 83.2% on time here.
Cancellations sit at 2.02% against a national 1.80%, which is ordinary. Diversions add another 0.04%.
Connections and stage length
What a delay here actually costs
8.5% of arrivals land an hour or more late, close to the national 8.2%. 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.
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 75.4% on time across 4,908 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 4,900 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 91.1% on time and June 63.1%, a swing of 28 points. If the dates move at all, move them out of June before you think about anything else.
Common questions
IAH to ATL questions
How often is IAH to ATL delayed?
Roughly 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 22.9% of the 4,900 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 ATL?
United Airlines leads at 81.9% on time across 1,236 flights. Frontier Airlines is at the other end on 60.3%, a gap of 22 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 ATL?
The 5am–8am departure window is the strongest at 83.2% on time. The 5pm–8pm window is the weakest at 67.5%, 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 June delays on IAH to ATL?
June is the weakest month at 63.1% on time, compared with 91.1% 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
- ATL to IAH — the return legseparate record
- George Bush Intercontinental (IAH) delay statistics
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- United Airlines on-time record81.9%
- Delta Air Lines on-time record79.9%
- Spirit Airlines 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. IAH to ATL and ATL 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.