Carrier route record

DLSFO→SEA

Delta Air Lines · San Francisco to Seattle

Flights: 924
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 SFO to SEA lands a B, 6 points better than the national rate of 77.6%. About one flight in six arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 924 flights. The strongest carrier on the route with a full sample, United Airlines, flew 2,042 at 75.8% on time.

Set against the rest of the country, Delta's SFO to SEA record is 6 points better than the US average of 77.6%. That gap is worth roughly 60 fewer late arrivals for every thousand flights.

On time

83.6%

Arrivals under 15 minutes late, of 907 completed flights

Avg delay

74 min

Across delayed arrivals only, not all flights

Cancelled

1.73%

National rate is 1.81%

Whole route

73.7%

Every carrier on SFO to SEA, 6,770 flights

These figures cover 924 flights between July 2025 and June 2026. The median arrival is 15 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

Delta against every carrier on SFO to SEA

Delta flew 924 of the 6,770 flights on SFO to SEA, about 14% of it. Its 83.6% on time is 10 points better than the route as a whole, which runs 73.7%. 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 Alaska at 69.1%. 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 75.8% of the time; Alaska Airlines manages 69.1%. Sample sizes sit next to every figure, because a two-point gap across 2,719 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)	924	83.6%	74 min	1.73%	B
United Airlines	2,042	75.8%	58 min	0.39%	B+
SkyWest Airlines	1,082	72.7%	50 min	1.11%	C
Alaska Airlines	2,719	69.1%	53 min	1.62%	C

United leads Alaska by 7 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

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 25 points, against 7 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am365 flights95.9%
8am–11am206 flights73.9%
11am–2pm188 flights71.0%
2pm–5pm161 flights83.3%
5pm–8pm—
8pm–5am4 flights—

Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.

The weak window here is the middle of the day, not the evening: 11am–2pm runs 71.0% on time against 95.9% for 5am–8am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. 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, May worst

Delays peak in May, when the on-time rate falls to 68.8%. March is the strongest month at 98.4%. Moving a flexible trip across that boundary buys 30 points. May was the busiest month here, with 93 flights.

Across the week, Monday is the strongest day at 87.7% on time and Thursday the weakest at 80.3%. 7 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. Late-arriving aircraft accounts for 67% of the 11,000 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.

Late-arriving aircraft
67%
Carrier
24%
National Airspace System
9%
Extreme weather
0%

67% 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 11,000 reported delay minutes here, that single category outweighs weather by 67 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 split is drawn from 11,014 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 95.9% on time here.

Cancellations sit at 1.73% against a national 1.81%, which is ordinary. Diversions add another 0.11%.

Connections and stage length

What a delay here costs

7.3% of arrivals land an hour or more late, close to the national 8.1%. 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 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. 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 67.3% on time across 923 flights, 16 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 16 points of difference.

One caution: this is a thin sample. 924 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. 924 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 83.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 907 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures