Carrier route record
DLSAN→BOS
Delta Air Lines · San Diego to Boston
- 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 SAN to BOS lands a B, 2 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 364 flights. The strongest carrier on the route with a full sample, JetBlue Airways, flew 919 at 79.3% on time.
The US average over the same twelve months is 77.6%, 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
79.3%
Arrivals under 15 minutes late, of 357 completed flights
Avg delay
86 min
Across delayed arrivals only, not all flights
Cancelled
1.65%
National rate is 1.81%
Whole route
77.9%
Every carrier on SAN to BOS, 1,818 flights
These figures cover 364 flights between July 2025 and June 2026. The median arrival is 8 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 SAN to BOS
Delta flew 364 of the 1,818 flights on SAN to BOS, about 20% of it. Its 79.3% on time is about level with the route as a whole at 77.9%. Ranked by on-time rate it is number two of four carriers on the route, where the range runs from JetBlue at 79.3% to Southwest at 44.4%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: 3 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 |
|---|---|---|---|---|---|
| JetBlue Airways | 919 | 79.3% | 99 min | 1.41% | B |
| Delta Air Lines (this page)thin sample | 364 | 79.3% | 86 min | 1.65% | B |
| Alaska Airlines | 508 | 76.2% | 66 min | 1.77% | B |
| Southwest Airlinesthin sample | 27 | 44.4% | 69 min | 0.00% | F+ |
No carrier stands out. JetBlue tops the table at 79.3%, 3 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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 79.3% on time across 364 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 364 flights scheduled in it.
Across the year
Delta on SAN to BOS through the year
Delays peak in March, when the on-time rate falls to 64.5%. August is the strongest month at 93.5%. Moving a flexible trip across that boundary buys 29 points. March was the busiest month here, with 31 flights.
Across the week, Monday is the strongest day at 86.0% on time and Sunday the weakest at 65.3%. 21 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 6,352 reported delay minutes.
- 36%Carrier
- 36%Late-arriving aircraft
- 27%National Airspace System
- 1%Extreme weather
36% 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 6,352 reported delay minutes here, that single category outweighs weather by 36 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 6,352 reported delay minutes.
The largest share of delay minutes, 36%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 2,311 of the 6,352 delay minutes reported here.
Cancellations sit at 1.65% against a national 1.81%, which is ordinary. Diversions add another 0.27%.
Connections and stage length
What a delay here costs
Badly late arrivals are rare here: only 3.4% land an hour or more behind schedule, against 8.1% 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 67.9% on time across 364 flights, 11 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 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 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 79.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 357 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
- JetBlue Airways on SAN to BOS79.3%
- Alaska Airlines on SAN to BOS76.2%
- 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.