Carrier route record
DLSEA→SFO
Delta Air Lines · Seattle to San Francisco
- Flights
- 985
- Period
- September 2025 to August 2026
- Share of route
- 14%
- Carriers
- 5
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on SEA to SFO draws a D. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is about 55 minutes behind schedule. Build slack into anything you connect to. That rests on 985 flights. The strongest carrier on the route with a full sample, SkyWest Airlines, flew 1,039 at 69.9% on time.
SkyWest Airlines is the most reliable of the three carriers covered here at 69.9% on time across 1,039 flights.
Key figures
On time
60.5%
Arrivals under 15 minutes late, of 968 completed flights
Avg delay
54 min
Across delayed arrivals only, not all flights
Cancelled
1.73%
National rate is 1.89%
Whole route
59.8%
Every carrier on SEA to SFO, 6,817 flights
These figures cover 985 flights between September 2025 and August 2026. Beyond the headline rate, 10.4% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Delta against every carrier on SEA to SFO
Delta flew 985 of the 6,817 flights on SEA to SFO, about 14% of it. Its 60.5% on time is about level with the route as a whole at 59.8%. 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 56.0%. 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 69.9% of the time; Alaska Airlines manages 56.0%. Sample sizes sit next to every figure, because a two-point gap across 2,727 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 | 1,039 | 69.9% | 52 min | 1.06% | C |
| Delta Air Lines (this page) | 985 | 60.5% | 54 min | 1.73% | D |
| United Airlines | 2,062 | 59.1% | 67 min | 0.82% | D+ |
| Alaska Airlines | 2,727 | 56.0% | 52 min | 1.14% | D |
The spread between SkyWest and Alaska is 14 points, wide enough that it should decide the booking. On a hundred trips that is 14 more arrivals inside the on-time window.
Flight by flight
Delta flight numbers on SEA to SFO
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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 24 points, against 14 points between the best and worst carrier.
- 5am–8am268 flights50.0%
- 8am–11am226 flights53.1%
- 11am–2pm122 flights73.9%
- 2pm–5pm4 flights—
- 5pm–8pm14 flights—
- 8pm–5am351 flights68.6%
Scale runs 40% 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 50.0%. 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 351 flights scheduled in it.
Across the year
Delta on SEA to SFO through the year
July is the worst month at 28.6% on time, 56 points below March, the best at 84.6%. 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. May was the busiest month here, with 93 flights.
Across the week, Saturday is the strongest day at 70.1% on time and Monday the weakest at 54.6%, a spread of 15 points.
Arrival by arrival
How late Delta on SEA to SFO runs when it is late
The 382 late arrivals split 152 under half an hour, 129 between 30 and 60 minutes, and 101 an hour or more.
- 15+ min early156 flights16.1%
- Within 15 min430 flights44.4%
- 15–29 min late152 flights15.7%
- 30–59 min late129 flights13.3%
- 1–2 hours late73 flights7.5%
- 2+ hours late28 flights2.9%
Scale runs 0% to 100%.
Share of 968 completed flights by arrival against schedule.
Time lost at the gate mostly stays lost. Of 331 departures that left 15 minutes late or more, only 39 made it up before arrival. In the other direction, 90 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at SFO.
The worst days
Worst days for Delta on SEA to SFO
The latest arrival of the period was on 22 July 2026, 10 hours 49 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on five of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 22 July 2026 | 10 hours 49 minutes | Carrier |
| 26 December 2025 | 9 hours 44 minutes | Carrier |
| 23 January 2026 | 9 hours 44 minutes | Carrier |
| 5 October 2025 | 5 hours 44 minutes | Carrier |
| 12 July 2026 | 4 hours 6 minutes | Carrier |
Delay causes
Why Delta runs late on this route
National Airspace System accounts for 49% of the 21,000 delay minutes carriers reported here, and the remaining four split what is left.
- 49%National Airspace System
- 35%Carrier
- 15%Late-arriving aircraft
- 1%Extreme weather
49% 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 10,000 minutes out of 21,000, against a national NAS share of 21%. The split is drawn from 20,685 reported delay minutes.
The largest share of delay minutes, 35%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 7,298 of the 21,000 delay minutes reported here.
Cancellations sit at 1.73% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
10.4% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection 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.
The return leg is a different operation and performs like one: it runs 79.5% on time across 986 flights, 19 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 19 points of difference.
One caution: this is a thin sample. 985 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. 985 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 60.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 968 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 SFO69.9%
- United Airlines on SEA to SFO59.1%
- Alaska Airlines on SEA to SFO56.0%
- 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.