Route reliability record
IAH→SEA
Houston to Seattle
- Flights
- 2,095
- Period
- July 2025 to June 2026
- Distance
- 1,874 mi
- Carriers
- 2
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 55 minutes on average. That is a workable record, not a spotless one. That rests on 2,095 flights, of which Alaska Airlines flew 852 at 78.5% 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
77.5%
Arrivals under 15 minutes late, of 2,081 completed flights
Avg delay
54 min
Across delayed arrivals only, not all flights
Cancelled
0.53%
National rate is 1.81%
Best carrier
Alaska
78.5% on time across 852 flights
These figures cover 2,095 flights between July 2025 and June 2026. The median arrival is 4 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 SEA
The two carriers here are closely matched: 2 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Alaska Airlines | 852 | 78.5% | 51 min | 0.70% | B+ |
| United Airlines | 1,243 | 76.8% | 56 min | 0.40% | B+ |
No carrier stands out. Alaska tops the table at 78.5%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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 2 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am379 flights87.2%
- 8am–11am551 flights82.3%
- 11am–2pm—
- 2pm–5pm369 flights81.6%
- 5pm–8pm436 flights64.5%
- 8pm–5am360 flights71.2%
Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 64.5% on time, against 87.2% 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 8am–11am window is the busiest, with 551 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 24 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 67.1% on time, 24 points below April, the best at 90.7%. 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, Tuesday is the strongest day at 81.6% on time and Saturday the weakest at 73.9%. 8 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 25,000 reported delay minutes.
- 41%Late-arriving aircraft
- 28%Carrier
- 25%National Airspace System
- 6%Extreme weather
- 0%Security
41% 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 25,000 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 25,462 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 87.2% on time here.
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
6.3% 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 55 minutes kind, which a normal layover absorbs.
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 80.3% 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. April runs 90.7% on time and July 67.1%, a swing of 24 points. If the dates move at all, move them out of July before you think about anything else. 2,081 completed flights over 12 months sit behind that.
Common questions
IAH to SEA questions
How often is IAH to SEA 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 2,095 flights in this analysis, against 22.4% nationally. Delayed flights are late by about 55 minutes on average.
Which airline is most reliable on IAH to SEA?
Alaska Airlines leads at 78.5% on time across 852 flights. United Airlines is at the other end on 76.8%, a gap of 2 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 SEA?
The 5am–8am departure window is the strongest at 87.2% on time. The 5pm–8pm window is the weakest at 64.5%, 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 IAH to SEA?
July is the weakest month at 67.1% on time, compared with 90.7% in April. Across the year that is 24 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
- SEA to IAH — the return legseparate record
- George Bush Intercontinental (IAH) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Alaska Airlines on-time record78.5%
- United Airlines on-time record76.8%
- 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 SEA and SEA 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.