Carrier route record

UALAX→SEA

United Airlines · Los Angeles to Seattle

Flights: 395
Period: July 2025 to June 2026
Share of route: 5%
Carriers: 6

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.

United on LAX to SEA earns an A+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.6%. When something does go wrong the average delay runs roughly 45 minutes. That rests on 395 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 2,224 at 86.8% on time.

Delta Air Lines is the most reliable of the three carriers covered here at 86.8% on time across 2,224 flights.

On time

85.0%

Arrivals under 15 minutes late, of 393 completed flights

Avg delay

47 min

Across delayed arrivals only, not all flights

Cancelled

0.51%

National rate is 1.81%

Whole route

85.4%

Every carrier on LAX to SEA, 7,424 flights

These figures cover 395 flights between July 2025 and June 2026. The median arrival is 10 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 LAX to SEA

United flew 395 of the 7,424 flights on LAX to SEA, about 5% of it. Its 85.0% on time is about level with the route as a whole at 85.4%. Ranked by on-time rate it is number three of six carriers on the route, where the range runs from Delta at 86.8% to Frontier at 79.7%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The three 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.

On-time performance by carrier on LAX to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	2,224	86.8%	76 min	0.76%	A+
Alaska Airlines	3,279	85.2%	49 min	1.10%	A
United Airlines (this page)	395	85.0%	47 min	0.51%	A+
SkyWest Airlines	1,239	84.6%	82 min	0.65%	B+
American Airlinesthin sample	11	81.8%	159 min	0.00%	B+
Frontier Airlinesthin sample	276	79.7%	76 min	3.62%	B−

No carrier stands out. Delta tops the table at 86.8%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.

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 20 points, against 2 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am—
8am–11am104 flights97.1%
11am–2pm91 flights77.5%
2pm–5pm52 flights86.5%
5pm–8pm148 flights80.4%
8pm–5am—

Scale runs 70% to 100%. Rows with fewer than 30 flights show a dash.

The weak window here is the middle of the day, not the evening: 11am–2pm runs 77.5% on time against 97.1% for 8am–11am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 5pm–8pm window is the busiest, with 148 flights scheduled in it.

Across the year

United on LAX to SEA through the year

Jul–Sep 2025183 flights81.2%
Oct–Dec 202586 flights95.3%
Jan–Mar 20263 flights—
Apr–Jun 2026123 flights82.9%

Scale runs 75% to 100%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 85.0% on time across 395 flights.

United on LAX to SEA did not run the same all year. Its best quarter was Oct–Dec 2025 at 95.3% on time and its weakest Jul–Sep 2025 at 81.2%, a swing of 14 points on roughly 132 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.

Across the week, Tuesday is the strongest day at 92.7% on time and Friday the weakest at 75.5%. 17 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 57% of the 2,788 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
57%
Carrier
24%
National Airspace System
19%

57% 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 2,788 reported delay minutes here, that single category outweighs weather by 57 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 2,788 reported delay minutes.

The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 97.1% on time here.

Cancellations are rare at 0.51%, 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

Badly late arrivals are rare here: only 3.6% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

The 954 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 90.3% on time across 393 flights, 5 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 5 points of difference.

One caution: this is a thin sample. 395 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 LAX to SEA

Put together: treat all of this as provisional. 395 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 85.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 393 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