Carrier route record
DLSEA→SFO
Delta Air Lines · Seattle to San Francisco
- Flights
- 923
- Period
- July 2025 to June 2026
- Share of route
- 14%
- Carriers
- 5
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on SEA to SFO draws a C. About one flight in three arrives 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 923 flights. The strongest carrier on the route with a full sample, SkyWest Airlines, flew 1,081 at 75.4% on time.
SkyWest Airlines is the most reliable of the three carriers covered here at 75.4% on time across 1,081 flights.
Key figures
On time
67.3%
Arrivals under 15 minutes late, of 908 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
1.63%
National rate is 1.81%
Whole route
65.6%
Every carrier on SEA to SFO, 6,764 flights
These figures cover 923 flights between July 2025 and June 2026. Beyond the headline rate, 9.3% 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
Delta against every carrier on SEA to SFO
Delta flew 923 of the 6,764 flights on SEA to SFO, about 14% of it. Its 67.3% on time is 2 points better than the route as a whole, which runs 65.6%. Ranked by on-time rate it is number three of five carriers on the route, where the range runs from Southwest at 100.0% to Alaska at 60.3%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
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 (this page) | 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.
Flight by flight
Delta flight numbers on SEA to SFO
Departure window
When Delta runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 16 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am206 flights57.8%
- 8am–11am226 flights62.5%
- 11am–2pm122 flights73.9%
- 2pm–5pm4 flights—
- 5pm–8pm18 flights—
- 8pm–5am347 flights73.5%
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 11am–2pm slot at 73.9% on time, ahead of 5am–8am at 57.8%. 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 8pm–5am window is the busiest, with 347 flights scheduled in it.
Across the year
Delta on SEA to SFO through the year
Delays peak in May, when the on-time rate falls to 49.5%. March is the strongest month at 84.6%. Moving a flexible trip across that boundary buys 35 points. May was the busiest month here, with 93 flights.
Across the week, Saturday is the strongest day at 72.9% on time and Monday the weakest at 61.8%. 11 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Delta runs late on this route
One category carries most of the weight here. National Airspace System accounts for 43% of the 17,000 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.
- 43%National Airspace System
- 40%Carrier
- 16%Late-arriving aircraft
- 2%Extreme weather
43% 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 7,121 minutes out of 17,000, against a national NAS share of 21%. The split is drawn from 16,743 reported delay minutes.
The largest share of delay minutes, 40%, 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 6,634 of the 17,000 delay minutes reported here.
Cancellations sit at 1.63% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.3% 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 83.6% on time across 924 flights, 16 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 16 points of difference.
One caution: this is a thin sample. 923 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Delta on SEA to SFO
Put together: treat all of this as provisional. 923 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 67.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 908 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to SFO, every carrier
- Delta on SFO to SEA, the return leg
- SkyWest Airlines on SEA to SFO75.4%
- United Airlines on SEA to SFO66.5%
- Alaska Airlines on SEA to SFO60.3%
- Delta Air Lines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- San Francisco International (SFO) delay statistics
- Same route, different airline: where the carrier you pick matters most
- How often a connection fails at the major US hubs
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.