Carrier route record
DLSFO→BOS
Delta Air Lines · San Francisco to Boston
- Flights
- 899
- Period
- July 2025 to June 2026
- Share of route
- 19%
- 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 BOS sits in the middle of the pack with a B. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 899 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,866 at 79.1% on time.
The US average over the same twelve months is 77.6%, so there is little to separate Delta on SFO 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
75.1%
Arrivals under 15 minutes late, of 883 completed flights
Avg delay
73 min
Across delayed arrivals only, not all flights
Cancelled
1.45%
National rate is 1.81%
Whole route
76.9%
Every carrier on SFO to BOS, 4,674 flights
These figures cover 899 flights between July 2025 and June 2026. Beyond the headline rate, 8.0% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Carrier by carrier
Delta against every carrier on SFO to BOS
Delta flew 899 of the 4,674 flights on SFO to BOS, about 19% of it. Its 75.1% on time is 2 points worse than the route as a whole, which runs 76.9%. Ranked by on-time rate it is number four of five carriers on the route, where the range runs from United at 79.1% to Southwest at 0.0%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: 4 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 |
|---|---|---|---|---|---|
| United Airlines | 1,866 | 79.1% | 73 min | 1.02% | B |
| Alaska Airlinesthin sample | 234 | 77.3% | 57 min | 0.43% | B+ |
| JetBlue Airways | 1,674 | 75.4% | 76 min | 1.79% | B |
| Delta Air Lines (this page) | 899 | 75.1% | 73 min | 1.45% | B |
| Southwest Airlinesthin sample | 1 | 0.0% | 49 min | 0.00% | F+ |
No carrier stands out. United tops the table at 79.1%, 4 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Delta flight numbers on SFO to BOS
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 23 points, against 4 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am363 flights89.0%
- 8am–11am2 flights—
- 11am–2pm338 flights65.6%
- 2pm–5pm18 flights—
- 5pm–8pm—
- 8pm–5am178 flights69.3%
Scale runs 55% to 95%. 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 65.6% on time against 89.0% 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 363 flights scheduled in it.
Across the year
Delta on SFO to BOS through the year
June is the worst month at 57.7% on time, 29 points below December, the best at 86.3%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. June was the busiest month here, with 98 flights.
Across the week, Saturday is the strongest day at 85.1% on time and Monday the weakest at 70.3%. 15 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 16,000 reported delay minutes.
- 35%National Airspace System
- 33%Late-arriving aircraft
- 25%Carrier
- 6%Extreme weather
35% 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 5,638 minutes out of 16,000, against a national NAS share of 21%. The split is drawn from 15,976 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 89.0% on time here.
Cancellations sit at 1.45% against a national 1.81%, which is ordinary. Diversions add another 0.33%.
Connections and stage length
What a delay here costs
8.0% 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.
At 2,704 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 71.8% on time across 898 flights, 3 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 3 points of difference.
One caution: this is a thin sample. 899 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 BOS
Put together: treat all of this as provisional. 899 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 75.1% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 883 completed flights over 12 months sit behind that.
Related
Where to go next
- SFO to BOS, every carrier
- Delta on BOS to SFO, the return leg
- United Airlines on SFO to BOS79.1%
- Alaska Airlines on SFO to BOS77.3%
- JetBlue Airways on SFO to BOS75.4%
- Delta Air Lines network-wide record
- San Francisco International (SFO) delay statistics
- Boston Logan International (BOS) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.