Route reliability record
SEA→SAN
Seattle to San Diego
- Flights
- 4,575
- Period
- June 2025 to May 2026
- Distance
- 1,050 mi
- Carriers
- 4
This route lands a B, level with the national rate of 77.4%. Roughly one flight in four arrive 15 minutes late or worse, and those flights are late by roughly 45 minutes on average. That is a workable record, not a spotless one. That rests on 4,575 flights, of which Delta Air Lines flew 1,698 at 82.6% on time.
The US average over the same twelve months is 77.4%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
77.7%
Arrivals under 15 minutes late, of 4,502 completed flights
Avg delay
46 min
Across delayed arrivals only, not all flights
Cancelled
1.22%
National rate is 1.80%
Best carrier
Delta
82.6% on time across 1,698 flights
These figures cover 4,575 flights between June 2025 and May 2026. The median arrival is 4 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 SAN
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 82.6% of the time; Alaska Airlines manages 75.3%. Sample sizes sit next to every figure, because a two-point gap across 2,788 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SkyWest Airlinesthin sample | 1 | 100.0% | — | 0.00% | A+ |
| Delta Air Lines | 1,698 | 82.6% | 54 min | 0.88% | B+ |
| Alaska Airlines | 2,788 | 75.3% | 44 min | 1.47% | B |
| Southwest Airlinesthin sample | 88 | 59.1% | 43 min | 0.00% | D+ |
Delta leads Alaska by 7 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 24 points, against 7 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am718 flights91.4%
- 8am–11am741 flights79.9%
- 11am–2pm876 flights75.9%
- 2pm–5pm876 flights76.4%
- 5pm–8pm823 flights67.2%
- 8pm–5am541 flights77.9%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 91.4% of the time, against 67.2% for the evening window. That is 24 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on.
Across the year
When delays peak on this route
This route's year swings by 20 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.
December is the weak month at 68.4% on time, against 88.0% 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.
Across the week, Tuesday is the strongest day at 82.1% on time and Sunday the weakest at 72.0%. 10 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 47,000 reported delay minutes.
- 38%Carrier
- 30%Late-arriving aircraft
- 29%National Airspace System
- 2%Extreme weather
- 0%Security
The largest share of delay minutes, 38%, 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 18,000 of the 47,000 delay minutes reported here.
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 91.4% on time here.
Cancellations sit at 1.22% against a national 1.80%, which is ordinary. Diversions add another 0.37%.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.7% land an hour or more behind schedule, against 8.2% 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 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 80.5% on time across 4,573 flights, within 3 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 4,575 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 88.0% on time and December 68.4%, a swing of 20 points. If the dates move at all, move them out of December before you think about anything else.
Common questions
SEA to SAN questions
How often is SEA to SAN delayed?
Roughly one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.3% of the 4,575 flights in this analysis, against 22.6% nationally. Delayed flights are late by roughly 45 minutes on average.
Which airline is most reliable on SEA to SAN?
Delta Air Lines leads at 82.6% on time across 1,698 flights. Alaska Airlines is at the other end on 75.3%, a gap of 7 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 SAN?
The 5am–8am departure window is the strongest at 91.4% on time. The 5pm–8pm window is the weakest at 67.2%, 24 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 SAN?
December is the weakest month at 68.4% on time, compared with 88.0% in April. Across the year that is 20 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- SAN to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- San Diego International (SAN) delay statistics
- SkyWest Airlines on-time record100.0%
- Delta Air Lines on-time record82.6%
- Alaska Airlines on-time record75.3%
- The best time of day to fly, according to 7.05 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. SEA to SAN and SAN 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, June 2025 to May 2026. Updated monthly. How this data is collected.