Carrier route record

DLSFO→SEA

Delta Air Lines · San Francisco to Seattle

Flights: 986
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 SFO to SEA lands a B, 2 points better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That rests on 986 flights. The strongest carrier on the route with a full sample, United Airlines, flew 2,063 at 75.1% on time.

The US average over the same twelve months is 77.3%, so there is little to separate Delta on SFO to SEA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

79.5%

Arrivals under 15 minutes late, of 967 completed flights

Avg delay

70 min

Across delayed arrivals only, not all flights

Cancelled

1.83%

National rate is 1.89%

Whole route

72.3%

Every carrier on SFO to SEA, 6,821 flights

These figures cover 986 flights between September 2025 and August 2026. Beyond the headline rate, 8.0% 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 SFO to SEA

Delta flew 986 of the 6,821 flights on SFO to SEA, about 14% of it. Its 79.5% on time is 7 points better than the route as a whole, which runs 72.3%. Ranked by on-time rate it is number two of five carriers on the route, where the range runs from Southwest at 100.0% to SkyWest at 68.8%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. United Airlines arrives on time 75.1% of the time; SkyWest Airlines manages 68.8%. Sample sizes sit next to every figure, because a two-point gap across 1,040 flights means less than a ten-point one.

On-time performance by carrier on SFO to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Southwest Airlinesthin sample	3	100.0%	—	0.00%	A+
Delta Air Lines (this page)	986	79.5%	70 min	1.83%	B
United Airlines	2,063	75.1%	57 min	0.44%	B+
Alaska Airlines	2,729	68.8%	54 min	1.28%	C
SkyWest Airlines	1,040	68.8%	50 min	1.15%	C

United leads SkyWest by 6 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Flight by flight

Delta flight numbers on SFO to SEA

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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 30 points, against 6 points between the best and worst carrier.

5am–8am365 flights95.0%
8am–11am268 flights65.4%
11am–2pm159 flights70.3%
2pm–5pm190 flights77.8%
5pm–8pm—
8pm–5am4 flights—

Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 95.0% of the time, against 65.4% for the morning window. That is 30 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 365 flights scheduled in it.

Across the year

Delta on SFO to SEA through the year

Darker means more delays. Figures are on-time percentages.March best, July worst

July is the worst month at 62.0% on time, 36 points below March, the best at 98.4%. 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, Sunday is the strongest day at 83.8% on time and Thursday the weakest at 71.5%, a spread of 12 points.

Arrival by arrival

How late Delta on SFO to SEA runs when it is late

Delta on SFO to SEA often beats the schedule: 427 of 967 completed flights, 44%, arrived 15 minutes or more early. The 198 late arrivals split 63 under half an hour, 58 between 30 and 60 minutes, and 77 an hour or more.

15+ min early427 flights44.2%
Within 15 min342 flights35.4%
15–29 min late63 flights6.5%
30–59 min late58 flights6.0%
1–2 hours late54 flights5.6%
2+ hours late23 flights2.4%

Scale runs 0% to 100%.

Share of 967 completed flights by arrival against schedule.

44 of 215 late departures made up the time and arrived on time, 20% of them. 27 flights left on time and still arrived late.

The worst days

Worst days for Delta on SFO to SEA

The latest arrival of the period was on 27 July 2026, 10 hours 54 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). Three of the five worst days fell in July 2026.

The latest arrivals of Delta on SFO to SEA in the period
Date	Arrived late by	Largest filed cause
27 July 2026	10 hours 54 minutes	Carrier
27 July 2026	9 hours 41 minutes	Carrier
28 October 2025	6 hours 32 minutes	Carrier
23 July 2026	5 hours 46 minutes	Late-arriving aircraft
27 December 2025	5 hours 22 minutes	Late-arriving aircraft

Delay causes

Why Delta runs late on this route

Late-arriving aircraft accounts for 63% of the 14,000 delay minutes carriers reported here, and the remaining four split what is left.

Late-arriving aircraft
63%
Carrier
23%
National Airspace System
14%
Extreme weather
0%

63% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 14,000 reported delay minutes here, that single category outweighs weather by 63 to one. The split is drawn from 13,768 reported delay minutes.

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 95.0% on time here.

Cancellations sit at 1.83% against a national 1.89%, which is ordinary. Diversions add another 0.10%.

Connections and stage length

What a delay here costs

8.0% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last a little over an hour, 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.

The return leg is a different operation and performs like one: it runs 60.5% on time across 985 flights, 19 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 19 points of difference.

One caution: this is a thin sample. 986 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 SFO to SEA

Put together: treat all of this as provisional. 986 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 79.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 967 completed flights over 12 months sit behind that.

Where to go next

Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated 22 October 2026; recomputed monthly. How this data is collected.

Key figures