Carrier route record
UAIAD→SEA
United Airlines · Washington to Seattle
- Flights
- 688
- Period
- July 2025 to June 2026
- Share of route
- 37%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.
United on IAD to SEA lands a B+, 2 points better than the national rate of 77.6%. About one flight in five 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 688 flights, with a median arrival 6 minutes early.
The US average over the same twelve months is 77.6%, so there is little to separate United on IAD 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
79.7%
Arrivals under 15 minutes late, of 681 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
0.58%
National rate is 1.81%
Whole route
76.6%
Every carrier on IAD to SEA, 1,884 flights
These figures cover 688 flights between July 2025 and June 2026. The median arrival is 6 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 IAD to SEA
United flew 688 of the 1,884 flights on IAD to SEA, about 37% of it. Its 79.7% on time is 3 points better than the route as a whole, which runs 76.6%. Ranked by on-time rate it is first of three carriers on the route, where the range runs from United at 79.7% to Alaska at 73.7%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
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 |
|---|---|---|---|---|---|
| United Airlines (this page) | 688 | 79.7% | 62 min | 0.58% | B+ |
| Delta Air Linesthin sample | 361 | 77.2% | 93 min | 1.39% | B |
| Alaska Airlines | 835 | 73.7% | 53 min | 1.20% | C |
Flight by flight
United flight numbers on IAD 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 22 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–8am—
- 8am–11am118 flights84.5%
- 11am–2pm165 flights91.5%
- 2pm–5pm—
- 5pm–8pm358 flights74.0%
- 8pm–5am47 flights69.6%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 91.5% on time, ahead of 8pm–5am at 69.6%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 5pm–8pm window is the busiest, with 358 flights scheduled in it.
Across the year
United on IAD to SEA through the year
September is the best month on the calendar at 93.2% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. July was the busiest month here, with 122 flights.
Across the week, Saturday is the strongest day at 82.3% on time and Sunday the weakest at 75.8%. 7 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 8,486 reported delay minutes.
- 42%Carrier
- 32%National Airspace System
- 16%Late-arriving aircraft
- 10%Extreme weather
32% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 2,756 minutes out of 8,486, against a national NAS share of 21%. The split is drawn from 8,486 reported delay minutes.
The largest share of delay minutes, 42%, 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 3,559 of the 8,486 delay minutes reported here.
Cancellations are rare at 0.58%, 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
6.5% 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 2,305 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 86.5% on time across 690 flights, 7 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 7 points of difference.
One caution: this is a thin sample. 688 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking United on IAD to SEA
Put together: treat all of this as provisional. 688 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 79.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 681 completed flights over 12 months sit behind that.
Related
Where to go next
- IAD to SEA, every carrier
- United on SEA to IAD, the return leg
- Delta Air Lines on IAD to SEA77.2%
- Alaska Airlines on IAD to SEA73.7%
- United Airlines network-wide record
- Washington Dulles International (IAD) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- The best time of day to fly, according to 7.04 million flight records
- Worst months to fly in the US, ranked by the data
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.