Route reliability record
BOS→SFO
Boston to San Francisco
- Flights
- 4,817
- Period
- September 2025 to August 2026
- Distance
- 2,704 mi
- Carriers
- 5
This route sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 8 points worse than the national rate of 77.3%. The late ones land about an hour behind schedule. That rests on 4,817 BOS to SFO flights, of which United Airlines flew 1,940 at 72.5% on time.
Best time to fly BOS to SFO: a 5am–8am departure, ideally on a Saturday. Flights in that window arrived on time 83.5% of the time and Saturday flights 76.9%, against 69.2% for the route overall.
United Airlines is the most reliable of the three carriers covered here at 72.5% on time across 1,940 flights.
Key figures
On time
69.2%
Arrivals under 15 minutes late, of 4,725 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
1.58%
National rate is 1.89%
Best carrier
United
72.5% on time across 1,940 flights
These figures cover 4,817 flights between September 2025 and August 2026. Beyond the headline rate, 11.1% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Which airline is most reliable on BOS to SFO
The choice of carrier is not cosmetic here. United Airlines arrives on time 72.5% of the time; JetBlue Airways manages 66.5%. Sample sizes sit next to every figure, because a two-point gap across 1,808 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlinesthin sample | 1 | 100.0% | — | 0.00% | A+ |
| United Airlines | 1,940 | 72.5% | 66 min | 1.19% | C |
| Delta Air Lines | 945 | 69.0% | 63 min | 1.59% | C |
| JetBlue Airways | 1,808 | 66.5% | 67 min | 2.05% | C |
| Alaska Airlinesthin sample | 123 | 57.6% | 76 min | 0.81% | D+ |
United leads JetBlue by 6 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Flights on BOS to SFO
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly Boston to San Francisco
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. BOS → SFOBoston to San Francisco | United Airlines | 71.6% | 72.5% | 1.19% | 5am–8am, Sat | UA 2441 06:00 |
| 2. BOS → SFOBoston to San Francisco | Delta Air Lines | 67.9% | 69.0% | 1.59% | 5am–8am, Sat | DL 1655 17:05 |
| 3. BOS → SFOBoston to San Francisco | JetBlue Airways | 65.1% | 66.5% | 2.05% | 5am–8am, Sat | B6 733 17:20 |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 29 points, against 6 points between the best and worst carrier.
- 5am–8am1,118 flights83.5%
- 8am–11am897 flights75.2%
- 11am–2pm445 flights74.4%
- 2pm–5pm710 flights65.4%
- 5pm–8pm986 flights54.6%
- 8pm–5am661 flights59.1%
Scale runs 45% to 90%.
The 5pm–8pm window is where this operation falls apart: 54.6% on time, against 83.5% 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 5am–8am window is the busiest, with 1,118 flights scheduled in it.
Explore
Filter BOS to SFO by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On BOS to SFO, the best departure window is 5am–8am at 83.5% on time and the worst is 5pm–8pm at 54.6%, a wide gap of 28.9 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am83.5%
- 8–11am75.2%
- 11am–2pm74.4%
- 2–5pm65.4%
- 5–8pm54.6%
- 8pm–5am59.1%
best all US flightsScale 45% to 95%.
Across the year
When delays peak on this route
This route's year swings by 25 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
June is the worst month at 56.5% on time, 25 points below September, the best at 81.4%. 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. August was the busiest month here, with 513 flights.
Across the week, Saturday is the strongest day at 76.9% on time and Monday the weakest at 64.2%, a spread of 13 points.
Delay causes
Why this route gets delayed
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 96,000 reported delay minutes.
- 41%National Airspace System
- 34%Late-arriving aircraft
- 22%Carrier
- 3%Extreme weather
- 0%Security
34% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 96,000 reported delay minutes here, that single category outweighs weather by 13 to one. The split is drawn from 96,335 reported delay minutes.
41% 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 40,000 minutes out of 96,000, against a national NAS share of 21%.
Cancellations sit at 1.58% against a national 1.89%, which is ordinary. Diversions add another 0.33%.
Connections and stage length
What a delay here actually costs
11.1% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection here, and two hours if the onward flight is on a separate ticket.
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 74.5% on time across 4,815 flights, 5 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 5 points of difference.
The sample behind these figures is 4,817 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in SFO after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 81.4% on time and June 56.5%, a swing of 25 points. If the dates move at all, move them out of June before you think about anything else. 4,725 completed flights over 12 months sit behind that.
Common questions
BOS to SFO questions
How often is BOS to SFO delayed?
Roughly one flight in three arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 30.8% of the 4,817 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on BOS to SFO?
United Airlines leads at 72.5% on time across 1,940 flights. JetBlue Airways is at the other end on 66.5%, a gap of 6 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on BOS to SFO?
The 5am–8am departure window is the strongest at 83.5% on time. The 5pm–8pm window is the weakest at 54.6%, 29 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are June delays on BOS to SFO?
June is the weakest month at 56.5% on time, compared with 81.4% in September. Across the year that is 25 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- SFO to BOS — the return legseparate record
- Boston Logan International (BOS) delay statistics
- San Francisco International (SFO) delay statistics
- United Airlines on BOS to SFO72.5%
- Delta Air Lines on BOS to SFO69.0%
- JetBlue Airways on BOS to SFO66.5%
- Alaska Airlines on BOS to SFO57.6%
- BOS to DCA, a related route72.6%
- LAX to SFO, a related route60.1%
- BOS to ORD, a related route71.9%
- Southwest Airlines on-time record100.0%
- United Airlines on-time record72.5%
- Delta Air Lines on-time record69.0%
- Why the first flight of the morning is statistically safest
- How often a connection fails at the major US hubs
Direction matters. BOS to SFO and SFO to BOS are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.