Carrier route record
UAIAD→SEA
United Airlines · Washington to Seattle
- Flights
- 625
- Period
- September 2025 to August 2026
- Share of route
- 34%
- Carriers
- 3
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with United Airlines.
United on IAD to SEA lands a B+, 4 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 about an hour on average. That rests on 625 flights, with a median arrival 7 minutes early.
Set against the rest of the country, United's IAD to SEA record is 4 points better than the US average of 77.3%. That gap is worth roughly 40 fewer late arrivals for every thousand flights.
Key figures
On time
81.3%
Arrivals under 15 minutes late, of 620 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
0.48%
National rate is 1.89%
Whole route
77.7%
Every carrier on IAD to SEA, 1,821 flights
These figures cover 625 flights between September 2025 and August 2026. The median arrival is 7 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
United against every carrier on IAD to SEA
United flew 625 of the 1,821 flights on IAD to SEA, about 34% of it. Its 81.3% on time is 4 points better than the route as a whole, which runs 77.7%. Ranked by on-time rate it is first of three carriers on the route, where the range runs from United at 81.3% to Alaska at 75.4%. 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) | 625 | 81.3% | 66 min | 0.48% | B+ |
| Delta Air Linesthin sample | 361 | 76.6% | 88 min | 1.39% | B |
| Alaska Airlines | 835 | 75.4% | 53 min | 1.20% | B |
Flight by flight
United flight numbers on IAD to SEA
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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 16 points, against half a point between the best and worst carrier.
- 5am–8am—
- 8am–11am111 flights90.9%
- 11am–2pm165 flights89.1%
- 2pm–5pm—
- 5pm–8pm349 flights74.5%
- 8pm–5am—
Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 90.9% of the time, against 74.5% for the evening window. That is 16 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 349 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 89 flights.
Across the week, Saturday is the strongest day at 86.9% on time and Thursday the weakest at 76.0%, a spread of 11 points.
Arrival by arrival
How late United on IAD to SEA runs when it is late
United on IAD to SEA often beats the schedule: 204 of 620 completed flights, 33%, arrived 15 minutes or more early. The 116 late arrivals split 49 under half an hour, 34 between 30 and 60 minutes, and 33 an hour or more.
- 15+ min early204 flights32.9%
- Within 15 min300 flights48.4%
- 15–29 min late49 flights7.9%
- 30–59 min late34 flights5.5%
- 1–2 hours late18 flights2.9%
- 2+ hours late15 flights2.4%
Scale runs 0% to 100%.
Share of 620 completed flights by arrival against schedule.
16 of 76 late departures made up the time and arrived on time, 21% of them. In the other direction, 56 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at SEA.
The worst days
Worst days for United on IAD to SEA
The latest arrival of the period was on 4 July 2026, 8 hours 51 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 4 July 2026 | 8 hours 51 minutes | Carrier |
| 5 July 2026 | 6 hours 30 minutes | National Airspace System |
| 10 June 2026 | 6 hours 25 minutes | Carrier |
| 11 June 2026 | 5 hours 45 minutes | Carrier |
| 16 August 2026 | 5 hours 3 minutes | Carrier |
Delay causes
Why United runs late on this route
Carrier accounts for 44% of the 7,680 delay minutes carriers reported here, and the remaining four split what is left.
- 44%Carrier
- 35%National Airspace System
- 13%Late-arriving aircraft
- 8%Extreme weather
35% 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 2,674 minutes out of 7,680, against a national NAS share of 21%. The split is drawn from 7,680 reported delay minutes.
The largest share of delay minutes, 44%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 3,399 of the 7,680 delay minutes reported here.
Cancellations are rare at 0.48%, 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 costs
5.3% 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 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 91.4% on time across 626 flights, 10 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 10 points of difference.
One caution: this is a thin sample. 625 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. 625 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 81.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 620 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 SEA76.6%
- Alaska Airlines on IAD to SEA75.4%
- 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 7.05 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.