Carrier route record

DLBOS→SAN

Delta Air Lines · Boston to San Diego

Flights: 364
Period: July 2025 to June 2026
Share of route: 20%
Carriers: 4

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.

Delta on BOS to SAN draws a C. About one flight in three arrives at least 15 minutes late, and the typical late arrival is roughly 45 minutes behind schedule. Build slack into anything you connect to. That rests on 364 flights. The strongest carrier on the route with a full sample, JetBlue Airways, flew 919 at 84.9% on time.

The national on-time rate over the same period is 77.6%, so Delta on BOS to SAN runs 10 points behind the country as a whole. Across a thousand flights that is about 97 extra late arrivals.

On time

67.9%

Arrivals under 15 minutes late, of 352 completed flights

Avg delay

43 min

Across delayed arrivals only, not all flights

Cancelled

1.65%

National rate is 1.81%

Whole route

76.5%

Every carrier on BOS to SAN, 1,818 flights

These figures cover 364 flights between July 2025 and June 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.

Carrier by carrier

Delta against every carrier on BOS to SAN

Delta flew 364 of the 1,818 flights on BOS to SAN, about 20% of it. Its 67.9% on time is 9 points worse than the route as a whole, which runs 76.5%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from JetBlue at 84.9% to Southwest at 29.6%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. JetBlue Airways arrives on time 84.9% of the time; Alaska Airlines manages 69.8%. Sample sizes sit next to every figure, because a two-point gap across 508 flights means less than a ten-point one.

On-time performance by carrier on BOS to SAN
Airline	Flights	On time	Avg delay	Cancelled	Grade
JetBlue Airways	919	84.9%	64 min	1.20%	B
Alaska Airlines	508	69.8%	56 min	1.57%	C
Delta Air Lines (this page)thin sample	364	67.9%	43 min	1.65%	C
Southwest Airlinesthin sample	27	29.6%	72 min	0.00%	F+

The spread between JetBlue 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 BOS to SAN

DL 57117:3567.9% · 364 flights

Departure window

When Delta runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 364 flights.

There are not enough flights in each departure window to split Delta's BOS to SAN record by time of day without the percentages moving on noise. The headline rate of 67.9% is the reliable figure here.

Across the year

Delta on BOS to SAN through the year

Jul–Sep 202592 flights66.7%
Oct–Dec 202591 flights66.7%
Jan–Mar 202690 flights72.6%
Apr–Jun 202691 flights65.9%

Scale runs 55% to 80%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 67.9% on time across 364 flights.

Quarter by quarter Delta on BOS to SAN held fairly steady: 66.7% in Jul–Sep 2025, 66.7% in Oct–Dec 2025, 72.6% in Jan–Mar 2026 and 65.9% in Apr–Jun 2026. A spread of 7 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.

Across the week, Thursday is the strongest day at 75.5% on time and Friday the weakest at 59.6%. 16 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Delta runs late on this route

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 4,798 reported delay minutes.

National Airspace System
42%
Late-arriving aircraft
32%
Carrier
26%
Extreme weather
0%

42% 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 2,004 minutes out of 4,798, against a national NAS share of 21%. The split is drawn from 4,798 reported delay minutes.

Cancellations sit at 1.65% against a national 1.81%, which is ordinary. Diversions add another 1.65%.

Connections and stage length

What a delay here costs

6.8% 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 roughly 45 minutes, which a normal layover absorbs.

At 2,588 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 79.3% on time across 364 flights, 11 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 11 points of difference.

One caution: this is a thin sample. 364 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 BOS to SAN

Put together: treat all of this as provisional. 364 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 67.9% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 352 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