Route reliability record

IAH→MIA

Houston to Miami

Flights: 3,736
Period: July 2025 to June 2026
Distance: 964 mi
Carriers: 6

This route lands a B, level with the national rate of 77.6%. Roughly one flight in five arrive 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 3,736 flights, of which United Airlines flew 1,479 at 80.3% on time.

United Airlines is the most reliable of the three carriers covered here at 80.3% on time across 1,479 flights.

On time

77.8%

Arrivals under 15 minutes late, of 3,683 completed flights

Avg delay

89 min

Across delayed arrivals only, not all flights

Cancelled

1.15%

National rate is 1.81%

Best carrier

United

80.3% on time across 1,479 flights

These figures cover 3,736 flights between July 2025 and June 2026. Beyond the headline rate, 8.7% 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 MIA

The choice of carrier is not cosmetic here. United Airlines arrives on time 80.3% of the time; Spirit Airlines manages 70.7%. Sample sizes sit next to every figure, because a two-point gap across 441 flights means less than a ten-point one.

On-time performance by carrier on IAH to MIA
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,479	80.3%	61 min	0.41%	B+
Envoy Airthin sample	122	78.5%	52 min	0.00%	B+
American Airlines	1,526	78.3%	111 min	1.31%	B
Spirit Airlines	441	70.7%	79 min	3.17%	C−
Frontier Airlinesthin sample	154	68.9%	142 min	1.95%	C
Republic Airwaysthin sample	14	64.3%	173 min	0.00%	D+

Spirit Airlines cancels 3.2% 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 21 points, against 10 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,137 flights88.8%
8am–11am318 flights79.2%
11am–2pm645 flights79.4%
2pm–5pm505 flights72.7%
5pm–8pm1,021 flights67.5%
8pm–5am110 flights68.9%

Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 88.8% of the time, against 67.5% for the evening window. That is 21 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 1,137 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 18 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.October best, July worst

July is the worst month at 66.2% on time, 18 points below October, the best at 83.8%. 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. January was the busiest month here, with 341 flights.

Across the week, Tuesday is the strongest day at 83.4% on time and Sunday the weakest at 70.9%. 13 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 73,000 reported delay minutes.

Late-arriving aircraft
42%
Carrier
32%
National Airspace System
18%
Extreme weather
8%
Security
0%

42% 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 73,000 reported delay minutes here, that single category outweighs weather by 5 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 72,685 reported delay minutes.

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 88.8% on time here.

Cancellations sit at 1.15% against a national 1.81%, which is ordinary. Diversions add another 0.27%.

Connections and stage length

What a delay here actually costs

8.7% 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 an hour and a half kind, which a normal layover absorbs.

The 964 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 77.2% on time across 3,737 flights, within half 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 3,736 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. October runs 83.8% on time and July 66.2%, a swing of 18 points. If the dates move at all, move them out of July before you think about anything else. 3,683 completed flights over 12 months sit behind that.

Common questions

IAH to MIA questions

How often is IAH to MIA delayed?

Roughly one flight in five arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.2% of the 3,736 flights in this analysis, against 22.4% nationally. Delayed flights are late by an hour and a half on average.

Which airline is most reliable on IAH to MIA?

United Airlines leads at 80.3% on time across 1,479 flights. Spirit Airlines is at the other end on 70.7%, a gap of 10 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 MIA?

The 5am–8am departure window is the strongest at 88.8% on time. The 5pm–8pm window is the weakest at 67.5%, 21 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 IAH to MIA?

July is the weakest month at 66.2% on time, compared with 83.8% in October. Across the year that is 18 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 MIA and MIA 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