Route reliability record
SEA→SFO
Seattle to San Francisco
- Flights
- 6,761
- Period
- June 2025 to May 2026
- Distance
- 679 mi
- Carriers
- 5
This route sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 9 points worse than the national rate of 77.4%. The late ones land about an hour behind schedule. That rests on 6,761 flights, of which SkyWest Airlines flew 1,108 at 78.9% on time.
SkyWest Airlines is the most reliable of the four carriers covered here at 78.9% on time across 1,108 flights.
Key figures
On time
68.7%
Arrivals under 15 minutes late, of 6,677 completed flights
Avg delay
58 min
Across delayed arrivals only, not all flights
Cancelled
1.18%
National rate is 1.80%
Best carrier
SkyWest
78.9% on time across 1,108 flights
These figures cover 6,761 flights between June 2025 and May 2026. Beyond the headline rate, 9.6% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Carrier by carrier
Which airline is most reliable on SEA to SFO
The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 78.9% of the time; Alaska Airlines manages 62.1%. Sample sizes sit next to every figure, because a two-point gap across 2,744 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlinesthin sample | 4 | 100.0% | — | 0.00% | A+ |
| SkyWest Airlines | 1,108 | 78.9% | 53 min | 0.99% | B+ |
| United Airlines | 2,012 | 71.6% | 73 min | 0.75% | C+ |
| Delta Air Lines | 893 | 69.6% | 57 min | 1.79% | C |
| Alaska Airlines | 2,744 | 62.1% | 52 min | 1.38% | D |
The spread between SkyWest and Alaska is 17 points, wide enough that it should decide the booking. On a hundred trips that is 17 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 12 points, against 17 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,147 flights71.4%
- 8am–11am906 flights64.9%
- 11am–2pm1,425 flights73.1%
- 2pm–5pm851 flights74.9%
- 5pm–8pm1,592 flights63.1%
- 8pm–5am840 flights65.7%
Scale runs 55% to 80%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 63.1% on time, against 74.9% for the 2pm–5pm 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.
Across the year
When delays peak on this route
This route's year swings by 41 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.
Delays peak in May, when the on-time rate falls to 40.7%. March is the strongest month at 81.7%. Moving a flexible trip across that boundary buys 41 points.
Across the week, Tuesday is the strongest day at 75.8% on time and Sunday the weakest at 64.1%. 12 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. National Airspace System accounts for 48% of the 122,000 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.
- 48%National Airspace System
- 26%Carrier
- 22%Late-arriving aircraft
- 4%Extreme weather
- 0%Security
48% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 58,000 minutes out of 122,000, against a national NAS share of 21%.
Cancellations sit at 1.18% against a national 1.80%, which is ordinary. Diversions add another 0.06%.
Connections and stage length
What a delay here actually costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.6% of arrivals land a full hour or more behind schedule, against 8.2% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
The 679 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 74.2% on time across 6,768 flights, 6 points above 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 6 points of difference.
The sample behind these figures is 6,761 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. March runs 81.7% on time and May 40.7%, a swing of 41 points. If the dates move at all, move them out of May before you think about anything else.
Common questions
SEA to SFO questions
How often is SEA to SFO delayed?
About one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 31.3% of the 6,761 flights in this analysis, against 22.6% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SEA to SFO?
SkyWest Airlines leads at 78.9% on time across 1,108 flights. Alaska Airlines is at the other end on 62.1%, a gap of 17 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 SFO?
The 2pm–5pm departure window is the strongest at 74.9% on time. The 5pm–8pm window is the weakest at 63.1%, 12 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 May delays on SEA to SFO?
May is the weakest month at 40.7% on time, compared with 81.7% in March. Across the year that is 41 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
- SFO to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- San Francisco International (SFO) delay statistics
- Southwest Airlines on-time record100.0%
- SkyWest Airlines on-time record78.9%
- United Airlines on-time record71.6%
- The best time of day to fly, according to 7.05 million flight records
- Connecting flights: how much buffer the data says you need
Direction matters. SEA to SFO and SFO 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.