Route reliability record
SEA→IAH
Seattle to Houston
- Flights
- 2,071
- Period
- September 2025 to August 2026
- Distance
- 1,874 mi
- Carriers
- 2
This route earns a B+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.3%. When something does go wrong the average delay runs about an hour. That rests on 2,071 SEA to IAH flights, of which United Airlines flew 1,230 at 87.9% on time.
Best time to fly SEA to IAH: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 92.3% of the time and Tuesday flights 86.9%, against 84.0% for the route overall.
Set against the rest of the country, this route's record is 7 points better than the US average of 77.3%. That gap is worth roughly 67 fewer late arrivals for every thousand flights.
Key figures
On time
84.0%
Arrivals under 15 minutes late, of 2,060 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
0.29%
National rate is 1.89%
Best carrier
United
87.9% on time across 1,230 flights
These figures cover 2,071 flights between September 2025 and August 2026. The median arrival is 8 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.
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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 87.9% of the time; Alaska Airlines manages 78.2%. Sample sizes sit next to every figure, because a two-point gap across 841 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,230 | 87.9% | 78 min | 0.16% | A+ |
| Alaska Airlines | 841 | 78.2% | 47 min | 0.48% | B+ |
United leads Alaska by 10 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Flights on SEA to IAH
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.
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Best ways to make this trip
The most reliable ways to fly Seattle to Houston
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SEA → IAHSeattle to Houston | United Airlines | 87.8% | 87.9% | 0.16% | 5am–8am, Tue | UA 2135 07:00 |
| 2. SEA → IAHSeattle to Houston | Alaska Airlines | 77.8% | 78.2% | 0.48% | 5pm–8pm, Sat | AS 398 17:39 |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 17 points, against 10 points between the best and worst carrier.
- 5am–8am454 flights92.3%
- 8am–11am185 flights83.0%
- 11am–2pm445 flights75.5%
- 2pm–5pm121 flights82.6%
- 5pm–8pm393 flights86.2%
- 8pm–5am473 flights83.0%
Scale runs 65% to 100%.
The weak window here is the middle of the day, not the evening: 11am–2pm runs 75.5% on time against 92.3% 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 473 flights scheduled in it.
Explore
Filter SEA to IAH by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On SEA to IAH, the best departure window is 5am–8am at 92.3% on time and the worst is 11am–2pm at 75.5%, a wide gap of 16.8 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am92.3%
- 8–11am83.0%
- 11am–2pm75.5%
- 2–5pm82.6%
- 5–8pm86.2%
- 8pm–5am83.0%
best all US flightsScale 60% to 95%.
Across the year
When delays peak on this route
This route's year swings by 19 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.
December is the weak month at 75.0% on time, against 93.8% in February. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. July was the busiest month here, with 231 flights.
Across the week, Tuesday is the strongest day at 86.9% on time and Friday the weakest at 81.8%, a spread of 5 points.
Delay causes
Why this route gets delayed
Carrier accounts for 48% of the 20,000 delay minutes carriers reported here, and the remaining four split what is left.
- 48%Carrier
- 31%Late-arriving aircraft
- 20%National Airspace System
- 2%Extreme weather
- 0%Security
The largest share of delay minutes, 48%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 9,560 of the 20,000 delay minutes reported here. The split is drawn from 20,122 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 92.3% on time here.
Cancellations are rare at 0.29%, below the national 1.89% 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 3.4% land an hour or more behind schedule, against 8.3% 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 is a different operation and performs like one: it runs 80.7% on time across 2,072 flights, 3 points below 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 3 points of difference.
The sample behind these figures is 2,071 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.
Work out the risk of missing a connection in IAH after this flight
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 December 75.0%, a swing of 19 points. If the dates move at all, move them out of December before you think about anything else. 2,060 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 six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 16.0% of the 2,071 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SEA to IAH?
United Airlines leads at 87.9% on time across 1,230 flights. Alaska Airlines is at the other end on 78.2%, 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 92.3% on time. The 11am–2pm window is the weakest at 75.5%, 17 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 December delays on SEA to IAH?
December is the weakest month at 75.0% on time, compared with 93.8% in February. Across the year that is 19 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 SEA to IAH87.9%
- Alaska Airlines on SEA to IAH78.2%
- SEA to LAX, a related route82.0%
- ORD to IAH, a related route76.0%
- SEA to PHX, a related route78.2%
- United Airlines on-time record87.9%
- Alaska Airlines on-time record78.2%
- The best time of day to fly, according to 7.05 million flight records
- Worst months to fly in the US, ranked by the data
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.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.