Route reliability record
SEA→SFO
Seattle to San Francisco
- Flights
- 6,764
- Period
- July 2025 to June 2026
- Distance
- 679 mi
- Carriers
- 5
This route draws a C. About one flight in three arrive at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 6,764 flights, of which SkyWest Airlines flew 1,081 at 75.4% on time.
SkyWest Airlines is the most reliable of the four carriers covered here at 75.4% on time across 1,081 flights.
Key figures
On time
65.6%
Arrivals under 15 minutes late, of 6,679 completed flights
Avg delay
59 min
Across delayed arrivals only, not all flights
Cancelled
1.20%
National rate is 1.81%
Best carrier
SkyWest
75.4% on time across 1,081 flights
These figures cover 6,764 flights between July 2025 and June 2026. Beyond the headline rate, 10.6% 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 75.4% of the time; Alaska Airlines manages 60.3%. Sample sizes sit next to every figure, because a two-point gap across 2,716 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 | 1,081 | 75.4% | 53 min | 1.02% | B |
| Delta Air Lines | 923 | 67.3% | 56 min | 1.63% | C |
| United Airlines | 2,040 | 66.5% | 71 min | 0.83% | C+ |
| Alaska Airlines | 2,716 | 60.3% | 52 min | 1.40% | D |
The spread between SkyWest and Alaska 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 15 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,151 flights67.5%
- 8am–11am936 flights57.9%
- 11am–2pm1,390 flights72.0%
- 2pm–5pm878 flights72.9%
- 5pm–8pm1,595 flights59.4%
- 8pm–5am814 flights65.1%
Scale runs 50% to 80%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 2pm–5pm slot at 72.9% on time, ahead of 8am–11am at 57.9%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 5pm–8pm window is the busiest, with 1,595 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 43 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.
June is the worst month at 39.2% on time, 43 points below March, the best at 81.7%. 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 639 flights.
Across the week, Tuesday is the strongest day at 72.5% on time and Monday the weakest at 61.2%. 11 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 52% of the 134,000 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.
- 52%National Airspace System
- 23%Carrier
- 20%Late-arriving aircraft
- 4%Extreme weather
- 0%Security
52% 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 70,000 minutes out of 134,000, against a national NAS share of 21%. The split is drawn from 134,325 reported delay minutes.
Cancellations sit at 1.20% against a national 1.81%, 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. 10.6% of arrivals land a full hour or more behind schedule, against 8.1% 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 73.7% on time across 6,770 flights, 8 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 8 points of difference.
The sample behind these figures is 6,764 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 June 39.2%, a swing of 43 points. If the dates move at all, move them out of June before you think about anything else. 6,679 completed flights over 12 months sit behind that.
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 34.4% of the 6,764 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SEA to SFO?
SkyWest Airlines leads at 75.4% on time across 1,081 flights. Alaska Airlines is at the other end on 60.3%, 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 SFO?
The 2pm–5pm departure window is the strongest at 72.9% on time. The 8am–11am window is the weakest at 57.9%, 15 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 June delays on SEA to SFO?
June is the weakest month at 39.2% on time, compared with 81.7% in March. Across the year that is 43 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 record75.4%
- Delta Air Lines on-time record67.3%
- The best time of day to fly, according to 7.04 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, July 2025 to June 2026. Updated monthly. How this data is collected.