Route reliability record
BOS→SFO
Boston to San Francisco
- Flights
- 4,612
- Period
- June 2025 to May 2026
- Distance
- 2,704 mi
- Carriers
- 5
This route sits in the middle of the pack with a B. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.4%. The late ones land about an hour behind schedule. That rests on 4,612 flights, of which United Airlines flew 1,816 at 79.4% on time.
United Airlines is the most reliable of the three carriers covered here at 79.4% on time across 1,816 flights.
Key figures
On time
75.3%
Arrivals under 15 minutes late, of 4,546 completed flights
Avg delay
65 min
Across delayed arrivals only, not all flights
Cancelled
1.13%
National rate is 1.80%
Best carrier
United
79.4% on time across 1,816 flights
These figures cover 4,612 flights between June 2025 and May 2026. Beyond the headline rate, 8.3% 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
Which airline is most reliable on BOS to SFO
The three 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 | 1,816 | 79.4% | 67 min | 1.05% | B |
| Delta Air Lines | 882 | 74.0% | 63 min | 1.36% | C |
| JetBlue Airways | 1,619 | 73.6% | 65 min | 1.24% | C |
| Alaska Airlinesthin sample | 294 | 62.6% | 63 min | 0.34% | D+ |
No carrier stands out. United tops the table at 79.4%, 6 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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 23 points, against 6 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am993 flights85.1%
- 8am–11am923 flights85.2%
- 11am–2pm366 flights79.2%
- 2pm–5pm665 flights73.7%
- 5pm–8pm940 flights64.3%
- 8pm–5am725 flights62.7%
Scale runs 55% to 90%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 62.7% on time, against 85.2% for the 8am–11am 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.
Across the year
When delays peak on this route
This route's year swings by 19 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.
December is the weak month at 65.0% on time, against 84.4% in August. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days.
Across the week, Tuesday is the strongest day at 80.7% on time and Thursday the weakest at 71.0%. 10 points is a smaller lever than departure hour, but it is free.
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 73,000 reported delay minutes.
- 38%Late-arriving aircraft
- 34%National Airspace System
- 25%Carrier
- 2%Extreme weather
- 0%Security
38% 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 73,000 reported delay minutes here, that single category outweighs weather by 19 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.
34% 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 25,000 minutes out of 73,000, against a national NAS share of 21%.
Cancellations sit at 1.13% against a national 1.80%, which is ordinary. Diversions add another 0.30%.
Connections and stage length
What a delay here actually costs
8.3% of arrivals land an hour or more late, close to the national 8.2%. 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 are the about an hour kind, 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 runs 78.2% on time across 4,610 flights, within 3 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
The sample behind these figures is 4,612 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.
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. August runs 84.4% on time and December 65.0%, a swing of 19 points. If the dates move at all, move them out of December before you think about anything else.
Common questions
BOS to SFO questions
How often is BOS to SFO delayed?
About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 24.7% of the 4,612 flights in this analysis, against 22.6% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on BOS to SFO?
United Airlines leads at 79.4% on time across 1,816 flights. JetBlue Airways is at the other end on 73.6%, 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 8am–11am departure window is the strongest at 85.2% on time. The 8pm–5am window is the weakest at 62.7%, 23 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 December delays on BOS to SFO?
December is the weakest month at 65.0% on time, compared with 84.4% in August. Across the year that is 19 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
- Southwest Airlines on-time record100.0%
- United Airlines on-time record79.4%
- Delta Air Lines on-time record74.0%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
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.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, June 2025 to May 2026. Updated monthly. How this data is collected.