Carrier route record
UAIAH→SEA
United Airlines · Houston to Seattle
- Flights
- 1,243
- Period
- July 2025 to June 2026
- Share of route
- 59%
- Carriers
- 2
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.
United on IAH to SEA lands a B+, about a point worse than the national rate of 77.6%. About one flight in four 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 1,243 flights, with a median arrival 3 minutes early.
The US average over the same twelve months is 77.6%, so there is little to separate United on IAH to SEA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
76.8%
Arrivals under 15 minutes late, of 1,236 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
0.40%
National rate is 1.81%
Whole route
77.5%
Every carrier on IAH to SEA, 2,095 flights
These figures cover 1,243 flights between July 2025 and June 2026. The median arrival is 3 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
United against every carrier on IAH to SEA
United flew 1,243 of the 2,095 flights on IAH to SEA, most of the route. Its 76.8% on time is about level with the route as a whole at 77.5%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from Alaska at 78.5% to United at 76.8%.
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 |
|---|---|---|---|---|---|
| Alaska Airlines | 852 | 78.5% | 51 min | 0.70% | B+ |
| United Airlines (this page) | 1,243 | 76.8% | 56 min | 0.40% | B+ |
Flight by flight
United flight numbers on IAH to SEA
Departure window
When United runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 18 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–8am35 flights88.2%
- 8am–11am406 flights80.8%
- 11am–2pm—
- 2pm–5pm299 flights79.6%
- 5pm–8pm143 flights70.6%
- 8pm–5am360 flights71.2%
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 88.2% of the time, against 70.6% for the evening window. That is 18 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 406 flights scheduled in it.
Across the year
United on IAH to SEA through the year
July is the worst month at 64.8% on time, 25 points below April, the best at 90.0%. 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 144 flights.
Across the week, Tuesday is the strongest day at 84.2% on time and Sunday the weakest at 73.3%. 11 points is a smaller lever than departure hour, but it is free.
Delay causes
Why United runs late on this route
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 16,000 reported delay minutes.
- 39%Late-arriving aircraft
- 35%Carrier
- 20%National Airspace System
- 6%Extreme weather
39% 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 16,000 reported delay minutes here, that single category outweighs weather by 6 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 16,196 reported delay minutes.
The largest share of delay minutes, 35%, 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 5,644 of the 16,000 delay minutes reported here.
Cancellations are rare at 0.40%, 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 costs
7.6% 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 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 is a different operation and performs like one: it runs 84.5% on time across 1,243 flights, 8 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 8 points of difference.
The sample behind these figures is 1,243 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 United on IAH to SEA
Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 90.0% on time and July 64.8%, a swing of 25 points. If the dates move at all, move them out of July before you think about anything else. 1,236 completed flights over 12 months sit behind that.
Related
Where to go next
- IAH to SEA, every carrier
- United on SEA to IAH, the return leg
- Alaska Airlines on IAH to SEA78.5%
- United Airlines network-wide record
- George Bush Intercontinental (IAH) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.