Carrier route record

DLBOS→SAN

Delta Air Lines · Boston to San Diego

Flights: 364
Period: September 2025 to August 2026
Share of route: 19%
Carriers: 4

Historical statistics for September 2025 to August 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 82.4% on time.

The national on-time rate over the same period is 77.3%, so Delta on BOS to SAN runs 11 points behind the country as a whole. Across a thousand flights that is about 113 extra late arrivals.

On time

66.0%

Arrivals under 15 minutes late, of 353 completed flights

Avg delay

44 min

Across delayed arrivals only, not all flights

Cancelled

1.65%

National rate is 1.89%

Whole route

75.3%

Every carrier on BOS to SAN, 1,880 flights

These figures cover 364 flights between September 2025 and August 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.

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Carrier by carrier

Delta against every carrier on BOS to SAN

Delta flew 364 of the 1,880 flights on BOS to SAN, about 19% of it. Its 66.0% on time is 9 points worse than the route as a whole, which runs 75.3%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from JetBlue at 82.4% to Southwest at 44.8%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. JetBlue Airways arrives on time 82.4% of the time; Alaska Airlines manages 74.6%. 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	82.4%	69 min	1.96%	B
Alaska Airlines	508	74.6%	71 min	1.57%	C
Delta Air Lines (this page)thin sample	364	66.0%	44 min	1.65%	C
Southwest Airlinesthin sample	89	44.8%	67 min	2.25%	F

JetBlue leads Alaska by 8 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Flight by flight

Delta flight numbers on BOS to SAN

DL 57117:1066.0% · 364 flights

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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 66.0% is the reliable figure here.

Across the year

Delta on BOS to SAN through the year

Jul–Sep 202530 flights—
Oct–Dec 202591 flights66.7%
Jan–Mar 202690 flights72.6%
Apr–Jun 202691 flights65.9%
Jul–Sep 202662 flights62.9%

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 66.0% on time across 364 flights.

Quarter by quarter Delta on BOS to SAN held fairly steady: 66.7% in Oct–Dec 2025, 72.6% in Jan–Mar 2026, 65.9% in Apr–Jun 2026 and 62.9% in Jul–Sep 2026. A spread of 10 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.

Across the week, Monday is the strongest day at 70.6% on time and Friday the weakest at 57.7%, a spread of 13 points.

Arrival by arrival

How late Delta on BOS to SAN runs when it is late

The 120 late arrivals split 56 under half an hour, 37 between 30 and 60 minutes, and 27 an hour or more.

15+ min early78 flights22.1%
Within 15 min155 flights43.9%
15–29 min late56 flights15.9%
30–59 min late37 flights10.5%
1–2 hours late22 flights6.2%
2+ hours late5 flights1.4%

Scale runs 0% to 100%.

Share of 353 completed flights by arrival against schedule.

21 of 83 late departures made up the time and arrived on time, 25% of them. In the other direction, 58 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 SAN.

The worst days

Worst days for Delta on BOS to SAN

The latest arrival of the period was on 14 October 2025, 3 hours 18 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The five worst days are spread across October, September, August, January and March, with no single month standing out.

The latest arrivals of Delta on BOS to SAN in the period
Date	Arrived late by	Largest filed cause
14 October 2025	3 hours 18 minutes	Late-arriving aircraft
6 September 2025	2 hours 33 minutes	National Airspace System
7 August 2026	2 hours 33 minutes	National Airspace System
19 January 2026	2 hours 29 minutes	Carrier
14 March 2026	2 hours 13 minutes	Late-arriving aircraft

Delay causes

Why Delta runs late on this route

National Airspace System accounts for 49% of the 5,219 delay minutes carriers reported here, and the remaining four split what is left.

National Airspace System
49%
Late-arriving aircraft
31%
Carrier
20%
Extreme weather
0%

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 2,536 minutes out of 5,219, against a national NAS share of 21%. The split is drawn from 5,219 reported delay minutes.

Cancellations sit at 1.65% against a national 1.89%, which is ordinary. Diversions add another 1.37%.

Connections and stage length

What a delay here costs

7.6% 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 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 78.2% on time across 364 flights, 12 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 12 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 66.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 353 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