Carrier route record

DLIAH→ATL

Delta Air Lines · Houston to Atlanta

Flights: 2,507
Period: July 2025 to June 2026
Share of route: 51%
Carriers: 4

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.

Delta on IAH to ATL lands a B, 3 points better than the national rate of 77.6%. About one flight in five arrives 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 2,507 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,257 at 81.9% on time.

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

On time

80.2%

Arrivals under 15 minutes late, of 2,454 completed flights

Avg delay

66 min

Across delayed arrivals only, not all flights

Cancelled

2.07%

National rate is 1.81%

Whole route

77.5%

Every carrier on IAH to ATL, 4,906 flights

These figures cover 2,507 flights between July 2025 and June 2026. The median arrival is 6 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

Delta against every carrier on IAH to ATL

Delta flew 2,507 of the 4,906 flights on IAH to ATL, most of the route. Its 80.2% on time is 3 points better than the route as a whole, which runs 77.5%. Ranked by on-time rate it is number two of four carriers on the route, where the range runs from United at 81.9% to Frontier at 61.7%.

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 (this page)	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.

Flight by flight

Delta flight numbers on IAH to ATL

Departure window

When Delta runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 28 points, against 20 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am725 flights89.8%
8am–11am388 flights79.8%
11am–2pm517 flights80.2%
2pm–5pm405 flights74.2%
5pm–8pm437 flights71.4%
8pm–5am35 flights61.8%

Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 61.8% on time, against 89.8% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 725 flights scheduled in it.

Across the year

Delta on IAH to ATL through the year

Darker means more delays. Figures are on-time percentages.September best, March worst

September is the best month on the calendar at 93.8% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. May was the busiest month here, with 240 flights.

Across the week, Wednesday is the strongest day at 84.8% on time and Sunday the weakest at 73.4%. 11 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Delta runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 43% of the 32,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Late-arriving aircraft
43%
Carrier
36%
National Airspace System
18%
Extreme weather
2%

43% 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 32,000 reported delay minutes here, that single category outweighs weather by 26 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 32,175 reported delay minutes.

The largest share of delay minutes, 36%, 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 12,000 of the 32,000 delay minutes reported here.

Cancellations sit at 2.07% against a national 1.81%, which is ordinary. Diversions add another 0.04%.

Connections and stage length

What a delay here costs

6.7% 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 last about an hour, 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 is a different operation and performs like one: it runs 75.9% on time across 2,508 flights, 4 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 4 points of difference.

The sample behind these figures is 2,507 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 Delta on IAH to ATL

Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 93.8% on time and March 69.4%, a swing of 24 points. If the dates move at all, move them out of March before you think about anything else. 2,454 completed flights over 12 months sit behind that.

Where to go next

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures