Carrier route record
WNSJC→SEA
Southwest Airlines · San Jose to Seattle
- Flights
- 928
- Period
- July 2025 to June 2026
- Share of route
- 21%
- Carriers
- 5
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on SJC 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 45 minutes behind schedule. That rests on 928 flights. The strongest carrier on the route with a full sample, SkyWest Airlines, flew 1,563 at 89.5% on time.
The US average over the same twelve months is 77.6%, so there is little to separate Southwest on SJC to SEA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
75.6%
Arrivals under 15 minutes late, of 927 completed flights
Avg delay
45 min
Across delayed arrivals only, not all flights
Cancelled
0.00%
National rate is 1.81%
Whole route
83.3%
Every carrier on SJC to SEA, 4,368 flights
These figures cover 928 flights between July 2025 and June 2026. The median arrival is 3 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
Southwest against every carrier on SJC to SEA
Southwest flew 928 of the 4,368 flights on SJC to SEA, about 21% of it. Its 75.6% on time is 8 points worse than the route as a whole, which runs 83.3%. Ranked by on-time rate it is last of five carriers on the route, where the range runs from American at 100.0% to Southwest at 75.6%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 89.5% of the time; Alaska Airlines manages 82.0%. Sample sizes sit next to every figure, because a two-point gap across 1,874 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlinesthin sample | 2 | 100.0% | — | 0.00% | A+ |
| United Airlinesthin sample | 1 | 100.0% | — | 0.00% | A+ |
| SkyWest Airlines | 1,563 | 89.5% | 66 min | 0.19% | A+ |
| Alaska Airlines | 1,874 | 82.0% | 49 min | 1.65% | B |
| Southwest Airlines (this page) | 928 | 75.6% | 45 min | 0.00% | B+ |
SkyWest 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 matters more here than the choice of carrier. The gap between the best and worst window is 46 points, against 8 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am228 flights98.7%
- 8am–11am122 flights76.2%
- 11am–2pm127 flights65.4%
- 2pm–5pm122 flights85.2%
- 5pm–8pm183 flights65.6%
- 8pm–5am146 flights52.7%
Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 52.7% on time, against 98.7% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 228 flights scheduled in it.
Across the year
Southwest on SJC to SEA through the year
December is the weak month at 65.4% on time, against 92.3% in January. 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. July was the busiest month here, with 114 flights.
Across the week, Wednesday is the strongest day at 86.6% on time and Sunday the weakest at 60.8%. 26 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 56% of the 10,000 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.
- 56%Late-arriving aircraft
- 24%Carrier
- 20%National Airspace System
- 1%Extreme weather
56% 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 10,000 reported delay minutes here, that single category outweighs weather by 56 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 10,177 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 98.7% on time here.
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
5.0% 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 45 minutes, which a normal layover absorbs.
The 696 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 72.6% on time across 927 flights, 3 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 3 points of difference.
One caution: this is a thin sample. 928 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 SJC to SEA
Put together: treat all of this as provisional. 928 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 75.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 927 completed flights over 12 months sit behind that.
Related
Where to go next
- SJC to SEA, every carrier
- Southwest on SEA to SJC, the return leg
- SkyWest Airlines on SJC to SEA89.5%
- Alaska Airlines on SJC to SEA82.0%
- Southwest Airlines network-wide record
- Norman Y. Mineta San Jose International (SJC) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.