Route reliability record
SFO→SEA
San Francisco to Seattle
- Flights
- 6,768
- Period
- June 2025 to May 2026
- Distance
- 679 mi
- Carriers
- 5
This route sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.4%. The late ones land about 55 minutes behind schedule. That rests on 6,768 flights, of which Delta Air Lines flew 894 at 85.0% on time.
Delta Air Lines is the most reliable of the four carriers covered here at 85.0% on time across 894 flights.
Key figures
On time
74.2%
Arrivals under 15 minutes late, of 6,683 completed flights
Avg delay
55 min
Across delayed arrivals only, not all flights
Cancelled
1.18%
National rate is 1.80%
Best carrier
Delta
85.0% on time across 894 flights
These figures cover 6,768 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 SFO to SEA
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 85.0% of the time; Alaska Airlines manages 67.7%. Sample sizes sit next to every figure, because a two-point gap across 2,747 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlinesthin sample | 3 | 100.0% | — | 0.00% | A+ |
| Delta Air Lines | 894 | 85.0% | 78 min | 1.90% | A |
| United Airlines | 2,014 | 77.7% | 55 min | 0.30% | B+ |
| SkyWest Airlines | 1,110 | 75.2% | 50 min | 1.08% | B |
| Alaska Airlines | 2,747 | 67.7% | 53 min | 1.64% | C |
The spread between Delta 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 22 points, against 17 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am881 flights91.4%
- 8am–11am1,261 flights69.0%
- 11am–2pm992 flights76.4%
- 2pm–5pm1,459 flights73.7%
- 5pm–8pm1,158 flights70.1%
- 8pm–5am1,017 flights69.2%
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 69.0% for the morning window. That is 22 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 25 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 62.1%. March is the strongest month at 86.9%. Moving a flexible trip across that boundary buys 25 points.
Across the week, Tuesday is the strongest day at 79.3% on time and Friday the weakest at 69.8%. 10 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. Late-arriving aircraft accounts for 45% of the 95,000 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.
- 45%Late-arriving aircraft
- 27%Carrier
- 26%National Airspace System
- 3%Extreme weather
45% 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 95,000 reported delay minutes here, that single category outweighs weather by 15 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 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 1.18% against a national 1.80%, which is ordinary. Diversions add another 0.07%.
Connections and stage length
What a delay here actually costs
7.0% of arrivals land an hour or more late, close to the national 8.2%. 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 are the about 55 minutes kind, which a normal layover absorbs.
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 68.7% on time across 6,761 flights, 6 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 6 points of difference.
The sample behind these figures is 6,768 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 86.9% on time and May 62.1%, a swing of 25 points. If the dates move at all, move them out of May before you think about anything else.
Common questions
SFO to SEA questions
How often is SFO to SEA delayed?
About 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 25.8% of the 6,768 flights in this analysis, against 22.6% nationally. Delayed flights are late by about 55 minutes on average.
Which airline is most reliable on SFO to SEA?
Delta Air Lines leads at 85.0% on time across 894 flights. Alaska Airlines is at the other end on 67.7%, 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 SFO to SEA?
The 5am–8am departure window is the strongest at 91.4% on time. The 8am–11am window is the weakest at 69.0%, 22 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 SFO to SEA?
May is the weakest month at 62.1% on time, compared with 86.9% in March. Across the year that is 25 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
- SEA to SFO — the return legseparate record
- San Francisco International (SFO) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Southwest Airlines on-time record100.0%
- Delta Air Lines on-time record85.0%
- United Airlines on-time record77.7%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. SFO to SEA and SEA to SFO 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.