Carrier route record
UASFO→SEA
United Airlines · San Francisco to Seattle
- Flights
- 2,063
- Period
- September 2025 to August 2026
- Share of route
- 30%
- Carriers
- 5
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with United Airlines.
United on SFO to SEA sits in the middle of the pack with a B+. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.3%. The late ones land about an hour behind schedule. That rests on 2,063 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 986 at 79.5% on time.
Delta Air Lines is the most reliable of the three carriers covered here at 79.5% on time across 986 flights.
Key figures
On time
75.1%
Arrivals under 15 minutes late, of 2,053 completed flights
Avg delay
57 min
Across delayed arrivals only, not all flights
Cancelled
0.44%
National rate is 1.89%
Whole route
72.3%
Every carrier on SFO to SEA, 6,821 flights
These figures cover 2,063 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
United against every carrier on SFO to SEA
United flew 2,063 of the 6,821 flights on SFO to SEA, about 30% of it. Its 75.1% on time is 3 points better than the route as a whole, which runs 72.3%. Ranked by on-time rate it is number three of five carriers on the route, where the range runs from Southwest at 100.0% to SkyWest at 68.8%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 79.5% of the time; SkyWest Airlines manages 68.8%. Sample sizes sit next to every figure, because a two-point gap across 1,040 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlinesthin sample | 3 | 100.0% | — | 0.00% | A+ |
| Delta Air Lines | 986 | 79.5% | 70 min | 1.83% | B |
| United Airlines (this page) | 2,063 | 75.1% | 57 min | 0.44% | B+ |
| Alaska Airlines | 2,729 | 68.8% | 54 min | 1.28% | C |
| SkyWest Airlines | 1,040 | 68.8% | 50 min | 1.15% | C |
Delta leads SkyWest by 11 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
United flight numbers on SFO 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 21 points, against 11 points between the best and worst carrier.
- 5am–8am82 flights87.8%
- 8am–11am366 flights72.5%
- 11am–2pm319 flights83.2%
- 2pm–5pm544 flights74.3%
- 5pm–8pm355 flights78.5%
- 8pm–5am397 flights66.5%
Scale runs 60% to 95%.
Book the early departure. Flights leaving between 5am–8am arrive on time 87.8% of the time, against 66.5% for the overnight window. That is 21 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 544 flights scheduled in it.
Across the year
United on SFO to SEA through the year
June is the worst month at 58.2% on time, 28 points below March, the best at 86.4%. 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 209 flights.
Across the week, Saturday is the strongest day at 86.4% on time and Friday the weakest at 67.3%, a spread of 19 points.
Arrival by arrival
How late United on SFO to SEA runs when it is late
United on SFO to SEA often beats the schedule: 592 of 2,053 completed flights, 29%, arrived 15 minutes or more early. The 511 late arrivals split 189 under half an hour, 175 between 30 and 60 minutes, and 147 an hour or more.
- 15+ min early592 flights28.8%
- Within 15 min950 flights46.3%
- 15–29 min late189 flights9.2%
- 30–59 min late175 flights8.5%
- 1–2 hours late95 flights4.6%
- 2+ hours late52 flights2.5%
Scale runs 0% to 100%.
Share of 2,053 completed flights by arrival against schedule.
113 of 496 late departures made up the time and arrived on time, 23% of them. In the other direction, 128 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 SFO to SEA
The latest arrival of the period was on 26 June 2026, 8 hours 21 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). On three of the five worst days the largest share was filed as a late-arriving aircraft.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 26 June 2026 | 8 hours 21 minutes | Carrier |
| 7 December 2025 | 7 hours 15 minutes | Carrier |
| 10 June 2026 | 5 hours 5 minutes | Late-arriving aircraft |
| 5 November 2025 | 4 hours 34 minutes | Late-arriving aircraft |
| 5 November 2025 | 4 hours 30 minutes | Late-arriving aircraft |
Delay causes
Why United runs late on this route
Late-arriving aircraft accounts for 54% of the 29,000 delay minutes carriers reported here, and the remaining four split what is left.
- 54%Late-arriving aircraft
- 27%Carrier
- 19%National Airspace System
- 1%Extreme weather
54% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 29,000 reported delay minutes here, that single category outweighs weather by 54 to one. The split is drawn from 29,074 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 87.8% on time here.
Cancellations are rare at 0.44%, 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
7.2% 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.
The 679 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty.
The return leg is a different operation and performs like one: it runs 59.1% on time across 2,062 flights, 16 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 16 points of difference.
The sample behind these figures is 2,063 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 SFO to SEA
Put together: the calendar is the biggest lever here, not the carrier or the hour. March runs 86.4% on time and June 58.2%, a swing of 28 points. If the dates move at all, move them out of June before you think about anything else. 2,053 completed flights over 12 months sit behind that.
Related
Where to go next
- SFO to SEA, every carrier
- United on SEA to SFO, the return leg
- Delta Air Lines on SFO to SEA79.5%
- Alaska Airlines on SFO to SEA68.8%
- SkyWest Airlines on SFO to SEA68.8%
- United Airlines network-wide record
- San Francisco International (SFO) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Why the first flight of the morning is statistically safest
- Same route, different airline: where the carrier you pick matters most
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.