Route reliability record
IAH→SEA
Houston to Seattle
- Flights
- 2,072
- Period
- September 2025 to August 2026
- Distance
- 1,874 mi
- Carriers
- 2
This route lands a B+, 3 points better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 50 minutes on average. That rests on 2,072 IAH to SEA flights, of which Alaska Airlines flew 842 at 81.9% on time.
Best time to fly IAH to SEA: a 5am–8am departure, ideally on a Thursday. Flights in that window arrived on time 86.9% of the time and Thursday flights 84.7%, against 80.7% for the route overall.
The US average over the same twelve months is 77.3%, 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
80.7%
Arrivals under 15 minutes late, of 2,065 completed flights
Avg delay
52 min
Across delayed arrivals only, not all flights
Cancelled
0.24%
National rate is 1.89%
Best carrier
Alaska
81.9% on time across 842 flights
These figures cover 2,072 flights between September 2025 and August 2026. The median arrival is 5 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 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 | 842 | 81.9% | 52 min | 0.48% | B+ |
| United Airlines | 1,230 | 79.9% | 52 min | 0.08% | B+ |
No carrier stands out. Alaska tops the table at 81.9%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Flights on IAH to SEA
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 Houston to Seattle
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. IAH → SEAHouston to Seattle | Alaska Airlines | 81.5% | 81.9% | 0.48% | 2pm–5pm, Tue | AS 453 07:00 |
| 2. IAH → SEAHouston to Seattle | United Airlines | 79.8% | 79.9% | 0.08% | 8am–11am, Thu | UA 2456 19:57 |
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 15 points, against 2 points between the best and worst carrier.
- 5am–8am347 flights86.9%
- 8am–11am578 flights83.4%
- 11am–2pm21 flights—
- 2pm–5pm429 flights81.8%
- 5pm–8pm369 flights72.0%
- 8pm–5am328 flights76.3%
Scale runs 65% to 90%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 86.9% of the time, against 72.0% for the evening window. That is 15 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 578 flights scheduled in it.
Explore
Filter IAH to SEA 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 IAH to SEA, the best departure window is 5am–8am at 86.9% on time and the worst is 5pm–8pm at 72.0%, a wide gap of 14.9 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am86.9%
- 8–11am83.4%
- 11am–2pm—
- 2–5pm81.8%
- 5–8pm72.0%
- 8pm–5am76.3%
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 20 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 70.7% on time, against 90.7% in April. 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, Thursday is the strongest day at 84.7% on time and Saturday the weakest at 76.7%, a spread of 8 points.
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 21,000 reported delay minutes.
- 39%Late-arriving aircraft
- 30%Carrier
- 26%National Airspace System
- 5%Extreme weather
- 1%Security
39% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 21,000 reported delay minutes here, that single category outweighs weather by 7 to one. The split is drawn from 20,809 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 86.9% on time here.
Cancellations are rare at 0.24%, 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
5.0% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last roughly 50 minutes, 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 84.0% on time across 2,071 flights, 3 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 3 points of difference.
The sample behind these figures is 2,072 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 SEA 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. April runs 90.7% on time and December 70.7%, a swing of 20 points. If the dates move at all, move them out of December before you think about anything else. 2,065 completed flights over 12 months sit behind that.
Common questions
IAH to SEA questions
How often is IAH to SEA 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 19.3% of the 2,072 flights in this analysis, against 22.7% nationally. Delayed flights are late by roughly 50 minutes on average.
Which airline is most reliable on IAH to SEA?
Alaska Airlines leads at 81.9% on time across 842 flights. United Airlines is at the other end on 79.9%, 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 86.9% on time. The 5pm–8pm window is the weakest at 72.0%, 15 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 IAH to SEA?
December is the weakest month at 70.7% on time, compared with 90.7% in April. Across the year that is 20 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 IAH to SEA81.9%
- United Airlines on IAH to SEA79.9%
- IAH to ORD, a related route75.1%
- LAX to SEA, a related route85.0%
- IAH to DFW, a related route76.4%
- Alaska Airlines on-time record81.9%
- United Airlines on-time record79.9%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 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.
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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.