Carrier route record

UASFO→SEA

United Airlines · San Francisco to Seattle

Flights: 2,042
Period: July 2025 to June 2026
Share of route: 30%
Carriers: 5

Historical statistics for July 2025 to June 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 77.6%. The late ones land about an hour behind schedule. That rests on 2,042 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 924 at 83.6% on time.

Delta Air Lines is the most reliable of the three carriers covered here at 83.6% on time across 924 flights.

On time

75.8%

Arrivals under 15 minutes late, of 2,034 completed flights

Avg delay

58 min

Across delayed arrivals only, not all flights

Cancelled

0.39%

National rate is 1.81%

Whole route

73.7%

Every carrier on SFO to SEA, 6,770 flights

These figures cover 2,042 flights between July 2025 and June 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.

Carrier by carrier

United against every carrier on SFO to SEA

United flew 2,042 of the 6,770 flights on SFO to SEA, about 30% of it. Its 75.8% on time is 2 points better than the route as a whole, which runs 73.7%. 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 Alaska at 69.1%. 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 83.6% of the time; Alaska Airlines manages 69.1%. Sample sizes sit next to every figure, because a two-point gap across 2,719 flights means less than a ten-point one.

On-time performance by carrier on SFO to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Southwest Airlinesthin sample	3	100.0%	—	0.00%	A+
Delta Air Lines	924	83.6%	74 min	1.73%	B
United Airlines (this page)	2,042	75.8%	58 min	0.39%	B+
SkyWest Airlines	1,082	72.7%	50 min	1.11%	C
Alaska Airlines	2,719	69.1%	53 min	1.62%	C

The spread between Delta and Alaska is 15 points, wide enough that it should decide the booking. On a hundred trips that is 15 more arrivals inside the on-time window.

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 28 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am72 flights93.1%
8am–11am366 flights73.3%
11am–2pm367 flights81.3%
2pm–5pm493 flights77.5%
5pm–8pm352 flights78.1%
8pm–5am392 flights65.4%

Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 93.1% of the time, against 65.4% for the overnight window. That is 28 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 493 flights scheduled in it.

Across the year

United on SFO to SEA through the year

Darker means more delays. Figures are on-time percentages.March best, June worst

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 198 flights.

Across the week, Saturday is the strongest day at 87.0% on time and Friday the weakest at 68.7%. 18 points is a smaller lever than departure hour, but it is free.

Delay causes

Why United runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 51% of the 28,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Late-arriving aircraft
51%
Carrier
29%
National Airspace System
19%
Extreme weather
1%

51% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 28,000 reported delay minutes here, that single category outweighs weather by 51 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 28,428 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 93.1% on time here.

Cancellations are rare at 0.39%, 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

7.2% 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.

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. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.

The return leg is a different operation and performs like one: it runs 66.5% on time across 2,040 flights, 9 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 9 points of difference.

The sample behind these figures is 2,042 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. 2,034 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures