Route reliability record
IAH→SJU
Houston to San Juan
- Flights
- 946
- Period
- July 2025 to June 2026
- Distance
- 2,007 mi
- Carriers
- 2
This route 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 946 IAH to SJU flights, with a median arrival 7 minutes early.
Best time to fly IAH to SJU: a 2pm–5pm departure, ideally on a Tuesday. Flights in that window arrived on time 86.6% of the time and Tuesday flights 88.6%, against 81.0% for the route overall.
The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
81.0%
Arrivals under 15 minutes late, of 941 completed flights
Avg delay
57 min
Across delayed arrivals only, not all flights
Cancelled
0.53%
National rate is 1.81%
Best carrier
United
82.7% on time across 872 flights
These figures cover 946 flights between July 2025 and June 2026. The median arrival is 7 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 SJU
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 872 | 82.7% | 54 min | 0.34% | B+ |
| Spirit Airlinesthin sample | 74 | 59.7% | 75 min | 2.70% | D |
Flight by flight
Flights on IAH to SJU
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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 11 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am—
- 8am–11am387 flights75.9%
- 11am–2pm19 flights—
- 2pm–5pm388 flights86.6%
- 5pm–8pm9 flights—
- 8pm–5am143 flights84.5%
Scale runs 65% to 90%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 2pm–5pm slot at 86.6% on time, ahead of 8am–11am at 75.9%. 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 388 flights scheduled in it.
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.
August is the worst month at 65.6% on time, 28 points below April, the best at 93.3%. 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. July was the busiest month here, with 111 flights.
Across the week, Tuesday is the strongest day at 88.6% on time and Saturday the weakest at 73.2%. 15 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 10,000 reported delay minutes.
- 35%Late-arriving aircraft
- 31%Carrier
- 29%National Airspace System
- 5%Extreme weather
35% 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 10,000 reported delay minutes here, that single category outweighs weather by 7 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 10,257 reported delay minutes.
Cancellations are rare at 0.53%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here actually costs
5.8% 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 last about an hour, which a normal layover absorbs.
At 2,007 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.
The return leg is a different operation and performs like one: it runs 87.7% on time across 948 flights, 7 points above 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 7 points of difference.
One caution: this is a thin sample. 946 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
Work out the risk of missing a connection in SJU after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 946 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 81.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 941 completed flights over 12 months sit behind that.
Common questions
IAH to SJU questions
How often is IAH to SJU delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 19.0% of the 946 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is IAH to SJU compared with the rest of the country?
81.0% of flights arrive on time here against a national 77.6%, a difference of 3 points in its favour. That is worth a B+ on this site's grading scale.
What time of day has the fewest delays on IAH to SJU?
The 2pm–5pm departure window is the strongest at 86.6% on time. The 8am–11am window is the weakest at 75.9%, 11 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 August delays on IAH to SJU?
August is the weakest month at 65.6% on time, compared with 93.3% in April. 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
- SJU to IAH — the return legseparate record
- George Bush Intercontinental (IAH) delay statistics
- Luis Munoz Marin International (SJU) delay statistics
- IAH to ORD, a related route74.8%
- MCO to SJU, a related route73.0%
- IAH to DFW, a related route75.0%
- United Airlines on-time record82.7%
- Spirit Airlines on-time record59.7%
- 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. IAH to SJU and SJU to IAH are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.