Route reliability record

IAH→ATL

Houston to Atlanta

Flights: 4,906
Period: July 2025 to June 2026
Distance: 689 mi
Carriers: 4

This route lands a B, level with the national rate of 77.6%. Roughly 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 4,906 flights, of which United Airlines flew 1,257 at 81.9% on time.

United Airlines is the most reliable of the four carriers covered here at 81.9% on time across 1,257 flights.

On time

77.5%

Arrivals under 15 minutes late, of 4,810 completed flights

Avg delay

67 min

Across delayed arrivals only, not all flights

Cancelled

1.92%

National rate is 1.81%

Best carrier

United

81.9% on time across 1,257 flights

These figures cover 4,906 flights between July 2025 and June 2026. The median arrival is 5 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.

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 61.7%. Sample sizes sit next to every figure, because a two-point gap across 767 flights means less than a ten-point one.

On-time performance by carrier on IAH to ATL
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,257	81.9%	69 min	0.72%	B+
Delta Air Lines	2,507	80.2%	66 min	2.07%	B
Spirit Airlines	375	77.4%	58 min	4.27%	B−
Frontier Airlines	767	61.7%	68 min	2.22%	D

Spirit Airlines cancels 4.3% 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 20 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,530 flights84.2%
8am–11am469 flights80.3%
11am–2pm873 flights80.0%
2pm–5pm789 flights74.4%
5pm–8pm906 flights67.4%
8pm–5am339 flights71.8%

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 84.2% of the time, against 67.4% for the evening window. That is 17 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 1,530 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 25 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.September best, March worst

September is the best month on the calendar at 91.1% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. April was the busiest month here, with 466 flights.

Across the week, Wednesday is the strongest day at 83.1% on time and Sunday the weakest at 71.4%. 12 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 72,000 reported delay minutes.

Late-arriving aircraft
40%
Carrier
35%
National Airspace System
23%
Extreme weather
3%
Security
0%

40% 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 72,000 reported delay minutes here, that single category outweighs weather by 16 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 71,932 reported delay minutes.

The largest share of delay minutes, 35%, 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 25,000 of the 72,000 delay minutes reported here.

Cancellations sit at 1.92% against a national 1.81%, which is ordinary. Diversions add another 0.04%.

Connections and stage length

What a delay here actually costs

7.7% 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 76.4% on time across 4,914 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 4,906 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 March 65.9%, a swing of 25 points. If the dates move at all, move them out of March before you think about anything else. 4,810 completed flights over 12 months sit behind that.

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 22.5% of the 4,906 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on IAH to ATL?

United Airlines leads at 81.9% on time across 1,257 flights. Frontier Airlines is at the other end on 61.7%, 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 IAH to ATL?

The 5am–8am departure window is the strongest at 84.2% on time. The 5pm–8pm window is the weakest at 67.4%, 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 March delays on IAH to ATL?

March is the weakest month at 65.9% on time, compared with 91.1% in September. Across the year that is 25 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

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, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures