Route reliability record

SEA→LAX

Seattle to Los Angeles

Flights: 7,428
Period: July 2025 to June 2026
Distance: 954 mi
Carriers: 6

This route lands a B+, 6 points better than the national rate of 77.6%. About one flight in six arrive 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 7,428 flights, of which United Airlines flew 393 at 90.3% on time.

United Airlines is the most reliable of the four carriers covered here at 90.3% on time across 393 flights.

On time

83.4%

Arrivals under 15 minutes late, of 7,357 completed flights

Avg delay

59 min

Across delayed arrivals only, not all flights

Cancelled

0.92%

National rate is 1.81%

Best carrier

United

90.3% on time across 393 flights

These figures cover 7,428 flights between July 2025 and June 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.

Carrier by carrier

Which airline is most reliable on SEA to LAX

The choice of carrier is not cosmetic here. United Airlines arrives on time 90.3% of the time; Alaska Airlines manages 81.0%. Sample sizes sit next to every figure, because a two-point gap across 3,282 flights means less than a ten-point one.

On-time performance by carrier on SEA to LAX
Airline	Flights	On time	Avg delay	Cancelled	Grade
American Airlinesthin sample	11	90.9%	149 min	0.00%	A+
United Airlines	393	90.3%	98 min	0.00%	A+
SkyWest Airlines	1,241	86.3%	109 min	0.64%	A+
Delta Air Lines	2,225	84.5%	59 min	0.67%	B+
Alaska Airlines	3,282	81.0%	43 min	1.07%	B
Frontier Airlinesthin sample	276	78.9%	60 min	3.62%	B−

United leads Alaska by 9 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Departure window

The best time of day to leave

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 14 points, against 9 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,416 flights89.0%
8am–11am1,210 flights87.2%
11am–2pm1,173 flights84.1%
2pm–5pm1,031 flights83.4%
5pm–8pm1,635 flights80.1%
8pm–5am963 flights75.0%

Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 89.0% of the time, against 75.0% for the overnight window. That is 14 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 1,635 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 16 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.

Darker means more delays. Figures are on-time percentages.April best, December worst

December is the weak month at 73.8% on time, against 89.5% in April. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. May was the busiest month here, with 677 flights.

Across the week, Tuesday is the strongest day at 86.1% on time and Sunday the weakest at 80.4%. 6 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

One category carries most of the weight here. Carrier accounts for 51% of the 72,000 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.

Carrier
51%
Late-arriving aircraft
32%
National Airspace System
14%
Extreme weather
3%

The largest share of delay minutes, 51%, 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 37,000 of the 72,000 delay minutes reported here. The split is drawn from 72,456 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 89.0% on time here.

Cancellations sit at 0.92% against a national 1.81%, which is ordinary. Diversions add another 0.04%.

Connections and stage length

What a delay here actually costs

Badly late arrivals are rare here: only 4.4% 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 runs 85.4% on time across 7,424 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

The sample behind these figures is 7,428 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 this route

Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 89.5% on time and December 73.8%, a swing of 16 points. If the dates move at all, move them out of December before you think about anything else. 7,357 completed flights over 12 months sit behind that.

Common questions

SEA to LAX questions

How often is SEA to LAX delayed?

About one flight in six arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 16.6% of the 7,428 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on SEA to LAX?

United Airlines leads at 90.3% on time across 393 flights. Alaska Airlines is at the other end on 81.0%, a gap of 9 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.

What time of day has the fewest delays on SEA to LAX?

The 5am–8am departure window is the strongest at 89.0% on time. The 8pm–5am window is the weakest at 75.0%, 14 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.

How bad are December delays on SEA to LAX?

December is the weakest month at 73.8% on time, compared with 89.5% in April. Across the year that is 16 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. SEA to LAX and LAX to SEA are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures