Carrier route record

WNSEA→SAN

Southwest Airlines · Seattle to San Diego

Flights: 118
Period: July 2025 to June 2026
Share of route: 3%
Carriers: 4

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

Southwest on SEA to SAN earns a D+, which is as low as this site's scale goes for a reason. Only 55.9% of flights arrive inside the 15-minute window, 22 points worse than the national rate of 77.6%. Late arrivals average about 40 minutes. Treat any tight connection here as a coin flip. That rests on 118 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 1,700 at 82.6% on time.

The national on-time rate over the same period is 77.6%, so Southwest on SEA to SAN runs 22 points behind the country as a whole. Across a thousand flights that is about 217 extra late arrivals.

On time

55.9%

Arrivals under 15 minutes late, of 118 completed flights

Avg delay

41 min

Across delayed arrivals only, not all flights

Cancelled

0.00%

National rate is 1.81%

Whole route

77.3%

Every carrier on SEA to SAN, 4,584 flights

These figures cover 118 flights between July 2025 and June 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.

Carrier by carrier

Southwest against every carrier on SEA to SAN

Southwest flew 118 of the 4,584 flights on SEA to SAN, about 3% of it. Its 55.9% on time is 21 points worse than the route as a whole, which runs 77.3%. Ranked by on-time rate it is last of four carriers on the route, where the range runs from SkyWest at 100.0% to Southwest at 55.9%. 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 82.6% of the time; Alaska Airlines manages 75.0%. Sample sizes sit next to every figure, because a two-point gap across 2,765 flights means less than a ten-point one.

On-time performance by carrier on SEA to SAN
Airline	Flights	On time	Avg delay	Cancelled	Grade
SkyWest Airlinesthin sample	1	100.0%	—	0.00%	A+
Delta Air Lines	1,700	82.6%	53 min	0.94%	B+
Alaska Airlines	2,765	75.0%	44 min	1.45%	B
Southwest Airlines (this page)thin sample	118	55.9%	41 min	0.00%	D+

Delta leads Alaska by 8 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Departure window

When Southwest runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 118 flights.

5am–8am—
8am–11am—
11am–2pm62 flights54.8%
2pm–5pm56 flights57.1%
5pm–8pm—
8pm–5am—

Scale runs 45% to 65%. Rows with fewer than 30 flights show a dash.

The 2pm–5pm window is the strongest at 57.1% on time. The full set of windows spans 2 points.

Across the year

Southwest on SEA to SAN through the year

Jan–Mar 202627 flights—
Apr–Jun 202691 flights54.9%

Scale runs 45% to 60%. 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 55.9% on time across 118 flights.

Split by quarter, Southwest on SEA to SAN logged 27 flights in Jan–Mar 2026 and 91 flights in Apr–Jun 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 55.9% annual figure is the one to use.

Delay causes

Why Southwest runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 55% of the 2,109 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
55%
Carrier
31%
National Airspace System
15%

55% 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 2,109 reported delay minutes here, that single category outweighs weather by 55 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 2,109 reported delay minutes.

Cancellations are rare at 0.00%, below the national 1.81% and low enough to earn the plus on the grade. Almost no flights are called off; the risk here is arriving late, not not arriving.

Connections and stage length

What a delay here costs

5.1% 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 40 minutes, which a normal layover absorbs.

The 1,050 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 58.1% on time across 118 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.

One caution: this is a thin sample. 118 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 Southwest on SEA to SAN

Put together: treat all of this as provisional. 118 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 55.9% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 118 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