Route reliability record

SEA→SJC

Seattle to San Jose

Flights: 4,371
Period: July 2025 to June 2026
Distance: 696 mi
Carriers: 5

This route lands a B+, 4 points better than the national rate of 77.6%. Roughly one flight in five arrive 15 minutes late or worse, and those flights are late by roughly 50 minutes on average. That is a workable record, not a spotless one. That rests on 4,371 flights, of which SkyWest Airlines flew 1,562 at 88.0% on time.

SkyWest Airlines is the most reliable of the three carriers covered here at 88.0% on time across 1,562 flights.

On time

81.6%

Arrivals under 15 minutes late, of 4,335 completed flights

Avg delay

48 min

Across delayed arrivals only, not all flights

Cancelled

0.80%

National rate is 1.81%

Best carrier

SkyWest

88.0% on time across 1,562 flights

These figures cover 4,371 flights between July 2025 and June 2026. The median arrival is 6 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 SJC

The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 88.0% of the time; Southwest Airlines manages 72.6%. Sample sizes sit next to every figure, because a two-point gap across 927 flights means less than a ten-point one.

On-time performance by carrier on SEA to SJC
Airline	Flights	On time	Avg delay	Cancelled	Grade
American Airlinesthin sample	4	100.0%	—	0.00%	A+
United Airlinesthin sample	1	100.0%	—	0.00%	A+
SkyWest Airlines	1,562	88.0%	61 min	0.19%	A+
Alaska Airlines	1,877	80.6%	45 min	1.55%	B
Southwest Airlines	927	72.6%	45 min	0.32%	C+

The spread between SkyWest and Southwest 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

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

5am–8am384 flights92.2%
8am–11am963 flights89.3%
11am–2pm878 flights77.8%
2pm–5pm842 flights82.8%
5pm–8pm662 flights73.9%
8pm–5am642 flights75.2%

Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 92.2% of the time, against 73.9% for the evening window. That is 18 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 963 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 17 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, July worst

July is the worst month at 72.3% on time, 17 points below April, the best at 89.5%. 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 425 flights.

Across the week, Wednesday is the strongest day at 87.4% on time and Friday the weakest at 76.6%. 11 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 39,000 reported delay minutes.

Carrier
41%
Late-arriving aircraft
39%
National Airspace System
11%
Extreme weather
9%
Security
1%

39% 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 39,000 reported delay minutes here, that single category outweighs weather by 4 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 38,633 reported delay minutes.

The largest share of delay minutes, 41%, 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 16,000 of the 39,000 delay minutes reported here.

Cancellations are rare at 0.80%, 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 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 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 runs 83.3% on time across 4,368 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 4,371 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 July 72.3%, a swing of 17 points. If the dates move at all, move them out of July before you think about anything else. 4,335 completed flights over 12 months sit behind that.

Common questions

SEA to SJC questions

How often is SEA to SJC delayed?

Roughly one flight in five arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 18.4% of the 4,371 flights in this analysis, against 22.4% nationally. Delayed flights are late by roughly 50 minutes on average.

Which airline is most reliable on SEA to SJC?

SkyWest Airlines leads at 88.0% on time across 1,562 flights. Southwest Airlines is at the other end on 72.6%, a gap of 15 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 SJC?

The 5am–8am departure window is the strongest at 92.2% on time. The 5pm–8pm window is the weakest at 73.9%, 18 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 July delays on SEA to SJC?

July is the weakest month at 72.3% on time, compared with 89.5% in April. Across the year that is 17 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 SJC and SJC 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