Route reliability record
SEA→IAH
Seattle to Houston
- Flights
- 2,095
- Period
- July 2025 to June 2026
- Distance
- 1,874 mi
- Carriers
- 2
This route lands a B+, 3 points better than the national rate of 77.6%. About one flight in five 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 2,095 flights, of which United Airlines flew 1,243 at 84.5% on time.
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
80.3%
Arrivals under 15 minutes late, of 2,074 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
0.62%
National rate is 1.81%
Best carrier
United
84.5% on time across 1,243 flights
These figures cover 2,095 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 SEA to IAH
The choice of carrier is not cosmetic here. United Airlines arrives on time 84.5% of the time; Alaska Airlines manages 74.3%. Sample sizes sit next to every figure, because a two-point gap across 852 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,243 | 84.5% | 70 min | 0.56% | B+ |
| Alaska Airlines | 852 | 74.3% | 45 min | 0.70% | C+ |
United leads Alaska by 10 points. Real, but small enough that a better departure time on the weaker carrier can outweigh 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 23 points, against 10 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am449 flights89.4%
- 8am–11am185 flights84.7%
- 11am–2pm446 flights66.6%
- 2pm–5pm121 flights82.6%
- 5pm–8pm398 flights83.5%
- 8pm–5am496 flights79.8%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
The weak window here is the middle of the day, not the evening: 11am–2pm runs 66.6% on time against 89.4% for 5am–8am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 8pm–5am window is the busiest, with 496 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 30 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.
July is the worst month at 63.6% on time, 30 points below February, the best at 93.8%. 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. July was the busiest month here, with 236 flights.
Across the week, Wednesday is the strongest day at 84.8% on time and Friday the weakest at 75.0%. 10 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Carrier accounts for 43% of the 23,000 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.
- 43%Carrier
- 30%Late-arriving aircraft
- 25%National Airspace System
- 1%Extreme weather
- 0%Security
The largest share of delay minutes, 43%, 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 9,899 of the 23,000 delay minutes reported here. The split is drawn from 23,027 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 89.4% on time here.
Cancellations are rare at 0.62%, 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
Badly late arrivals are rare here: only 4.4% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
At 1,874 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 runs 77.5% on time across 2,095 flights, within 3 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 2,095 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. February runs 93.8% on time and July 63.6%, a swing of 30 points. If the dates move at all, move them out of July before you think about anything else. 2,074 completed flights over 12 months sit behind that.
Common questions
SEA to IAH questions
How often is SEA to IAH delayed?
About 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 19.7% of the 2,095 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SEA to IAH?
United Airlines leads at 84.5% on time across 1,243 flights. Alaska Airlines is at the other end on 74.3%, 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 SEA to IAH?
The 5am–8am departure window is the strongest at 89.4% on time. The 11am–2pm window is the weakest at 66.6%, 23 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 SEA to IAH?
July is the weakest month at 63.6% on time, compared with 93.8% in February. Across the year that is 30 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
- IAH to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- George Bush Intercontinental (IAH) delay statistics
- United Airlines on-time record84.5%
- Alaska Airlines on-time record74.3%
- The best time of day to fly, according to 7.04 million flight records
- Do budget airlines really get delayed more? The numbers
Direction matters. SEA to IAH and IAH to SEA 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.