Carrier route record
DLBOS→SFO
Delta Air Lines · Boston to San Francisco
- Flights
- 898
- 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 BOS to SFO sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 6 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 898 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,867 at 76.3% on time.
The national on-time rate over the same period is 77.6%, so Delta on BOS to SFO runs 6 points behind the country as a whole. Across a thousand flights that is about 58 extra late arrivals.
Key figures
On time
71.8%
Arrivals under 15 minutes late, of 882 completed flights
Avg delay
63 min
Across delayed arrivals only, not all flights
Cancelled
1.45%
National rate is 1.81%
Whole route
72.6%
Every carrier on BOS to SFO, 4,676 flights
These figures cover 898 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 BOS to SFO
Delta flew 898 of the 4,676 flights on BOS to SFO, about 19% of it. Its 71.8% on time is about level with the route as a whole at 72.6%. Ranked by on-time rate it is number three of five carriers on the route, where the range runs from Southwest at 100.0% to Alaska at 61.6%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: 6 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 |
|---|---|---|---|---|---|
| Southwest Airlinesthin sample | 1 | 100.0% | — | 0.00% | A+ |
| United Airlines | 1,867 | 76.3% | 66 min | 1.12% | B |
| Delta Air Lines (this page) | 898 | 71.8% | 63 min | 1.45% | C |
| JetBlue Airways | 1,676 | 70.5% | 65 min | 1.31% | C |
| Alaska Airlinesthin sample | 234 | 61.6% | 66 min | 0.43% | D+ |
No carrier stands out. United tops the table at 76.3%, 6 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 BOS to SFO
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 20 points, against 6 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am215 flights82.9%
- 8am–11am148 flights75.3%
- 11am–2pm6 flights—
- 2pm–5pm58 flights77.2%
- 5pm–8pm289 flights63.4%
- 8pm–5am182 flights68.7%
Scale runs 55% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 63.4% on time, against 82.9% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5pm–8pm window is the busiest, with 289 flights scheduled in it.
Across the year
Delta on BOS to SFO through the year
June is the worst month at 54.2% on time, 29 points below August, the best at 83.3%. 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, Friday is the strongest day at 73.7% on time and Sunday the weakest at 68.3%. 5 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Delta runs late on this route
One category carries most of the weight here. National Airspace System accounts for 43% of the 16,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 43%National Airspace System
- 31%Late-arriving aircraft
- 25%Carrier
- 0%Security
- 0%Extreme weather
43% 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 6,814 minutes out of 16,000, against a national NAS share of 21%. The split is drawn from 15,686 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 82.9% 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 about 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 75.1% on time across 899 flights, 3 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 3 points of difference.
One caution: this is a thin sample. 898 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 SFO
Put together: treat all of this as provisional. 898 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 71.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 882 completed flights over 12 months sit behind that.
Related
Where to go next
- BOS to SFO, every carrier
- Delta on SFO to BOS, the return leg
- United Airlines on BOS to SFO76.3%
- JetBlue Airways on BOS to SFO70.5%
- Alaska Airlines on BOS to SFO61.6%
- Delta Air Lines network-wide record
- Boston Logan International (BOS) delay statistics
- San Francisco International (SFO) delay statistics
- The best time of day to fly, according to 7.04 million flight records
- Connecting flights: how much buffer the data says you need
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.