Carrier route record
DLSAN→BOS
Delta Air Lines · San Diego to Boston
- 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 SAN to BOS lands a B, about a point better than the national rate of 77.3%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That rests on 364 flights. The strongest carrier on the route with a full sample, Alaska Airlines, flew 509 at 78.3% on time.
The US average over the same twelve months is 77.3%, so there is little to separate Delta on SAN to BOS from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
78.2%
Arrivals under 15 minutes late, of 358 completed flights
Avg delay
91 min
Across delayed arrivals only, not all flights
Cancelled
1.65%
National rate is 1.89%
Whole route
75.5%
Every carrier on SAN to BOS, 1,881 flights
These figures cover 364 flights between September 2025 and August 2026. The median arrival is 4 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.
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Carrier by carrier
Delta against every carrier on SAN to BOS
Delta flew 364 of the 1,881 flights on SAN to BOS, about 19% of it. Its 78.2% on time is 3 points better than the route as a whole, which runs 75.5%. Ranked by on-time rate it is number two of four carriers on the route, where the range runs from Alaska at 78.3% to Southwest at 38.2%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: 2 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Alaska Airlines | 509 | 78.3% | 72 min | 1.38% | B |
| Delta Air Lines (this page)thin sample | 364 | 78.2% | 91 min | 1.65% | B |
| JetBlue Airways | 919 | 76.6% | 92 min | 2.07% | B |
| Southwest Airlinesthin sample | 89 | 38.2% | 73 min | 0.00% | F+ |
No carrier stands out. Alaska tops the table at 78.3%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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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.
The overnight block holds up unusually well at 78.4% on time across 363 flights. Red-eyes fly into empty airspace and empty gates, and they are the first rotation of the aircraft's day rather than the last. The 8pm–5am window is the busiest, with 363 flights scheduled in it.
Across the year
Delta on SAN to BOS through the year
May is the best month on the calendar at 90.3% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. March was the busiest month here, with 31 flights.
Across the week, Monday is the strongest day at 86.3% on time and Sunday the weakest at 69.4%, a spread of 17 points.
Arrival by arrival
How late Delta on SAN to BOS runs when it is late
Delta on SAN to BOS often beats the schedule: 95 of 358 completed flights, 27%, arrived 15 minutes or more early. The 78 late arrivals split 33 under half an hour, 31 between 30 and 60 minutes, and 14 an hour or more.
- 15+ min early95 flights26.5%
- Within 15 min185 flights51.7%
- 15–29 min late33 flights9.2%
- 30–59 min late31 flights8.7%
- 1–2 hours late6 flights1.7%
- 2+ hours late8 flights2.2%
Scale runs 0% to 100%.
Share of 358 completed flights by arrival against schedule.
25 of 84 late departures made up the time and arrived on time, 30% of them. In the other direction, 19 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 BOS.
The worst days
Worst days for Delta on SAN to BOS
The latest arrival of the period was on 7 March 2026, 17 hours 39 minutes behind schedule; most of its delay minutes were filed as national airspace system delay. On three of the five worst days the largest share was filed as carrier-caused (crew, maintenance, fuelling, baggage).
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 7 March 2026 | 17 hours 39 minutes | National Airspace System |
| 28 October 2025 | 14 hours 39 minutes | Late-arriving aircraft |
| 17 September 2025 | 11 hours 34 minutes | Carrier |
| 7 August 2026 | 10 hours 21 minutes | Carrier |
| 6 September 2025 | 8 hours 28 minutes | Carrier |
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 7,066 reported delay minutes.
- 41%Carrier
- 32%Late-arriving aircraft
- 26%National Airspace System
- 1%Extreme weather
The largest share of delay minutes, 41%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 2,931 of the 7,066 delay minutes reported here. The split is drawn from 7,066 reported delay minutes.
Cancellations sit at 1.65% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
Badly late arrivals are rare here: only 3.9% land an hour or more behind schedule, against 8.3% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
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 66.0% on time across 364 flights, 12 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 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 SAN to BOS
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 78.2% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 358 completed flights over 12 months sit behind that.
Related
Where to go next
- SAN to BOS, every carrier
- Delta on BOS to SAN, the return leg
- Alaska Airlines on SAN to BOS78.3%
- JetBlue Airways on SAN to BOS76.6%
- Delta Air Lines network-wide record
- San Diego International (SAN) delay statistics
- Boston Logan International (BOS) delay statistics
- Why the first flight of the morning is statistically safest
- Worst months to fly in the US, ranked by the data
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.