Route reliability record
SFO→BOS
San Francisco to Boston
- Flights
- 4,815
- Period
- September 2025 to August 2026
- Distance
- 2,704 mi
- Carriers
- 5
This route sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.3%. The late ones land a little over an hour behind schedule. That rests on 4,815 SFO to BOS flights, of which United Airlines flew 1,939 at 78.5% on time.
Best time to fly SFO to BOS: a 5am–8am departure, ideally on a Saturday. Flights in that window arrived on time 87.1% of the time and Saturday flights 82.7%, against 74.5% for the route overall.
United Airlines is the most reliable of the three carriers covered here at 78.5% on time across 1,939 flights.
Key figures
On time
74.5%
Arrivals under 15 minutes late, of 4,719 completed flights
Avg delay
74 min
Across delayed arrivals only, not all flights
Cancelled
1.81%
National rate is 1.89%
Best carrier
United
78.5% on time across 1,939 flights
These figures cover 4,815 flights between September 2025 and August 2026. Beyond the headline rate, 10.2% 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 SFO to BOS
The choice of carrier is not cosmetic here. United Airlines arrives on time 78.5% of the time; JetBlue Airways manages 71.5%. Sample sizes sit next to every figure, because a two-point gap across 1,806 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Alaska Airlinesthin sample | 123 | 80.3% | 63 min | 0.81% | B+ |
| United Airlines | 1,939 | 78.5% | 73 min | 1.08% | B |
| Delta Air Lines | 946 | 71.5% | 69 min | 1.59% | C |
| JetBlue Airways | 1,806 | 71.5% | 78 min | 2.77% | C |
| Southwest Airlinesthin sample | 1 | 0.0% | 49 min | 0.00% | F+ |
United leads JetBlue by 7 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Flights on SFO to BOS
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 San Francisco to Boston
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. SFO → BOSSan Francisco to Boston | United Airlines | 77.7% | 78.5% | 1.08% | 5am–8am, Sat | UA 1665 23:05 |
| 2. SFO → BOSSan Francisco to Boston | Delta Air Lines | 70.4% | 71.5% | 1.59% | 5am–8am, Sat | DL 400 07:10 |
| 3. SFO → BOSSan Francisco to Boston | JetBlue Airways | 69.5% | 71.5% | 2.77% | 5am–8am, Sat | B6 434 06:00 |
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 21 points, against 7 points between the best and worst carrier.
- 5am–8am785 flights87.1%
- 8am–11am872 flights73.5%
- 11am–2pm1,227 flights65.7%
- 2pm–5pm734 flights73.4%
- 5pm–8pm1 flights—
- 8pm–5am1,196 flights76.7%
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 65.7% on time against 87.1% 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 11am–2pm window is the busiest, with 1,227 flights scheduled in it.
Explore
Filter SFO to BOS 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 SFO to BOS, the best departure window is 5am–8am at 87.1% on time and the worst is 11am–2pm at 65.7%, a wide gap of 21.4 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am87.1%
- 8–11am73.5%
- 11am–2pm65.7%
- 2–5pm73.4%
- 5–8pm—
- 8pm–5am76.7%
best all US flightsScale 55% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 18 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.
July is the worst month at 67.1% on time, 18 points below February, the best at 84.6%. 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 82.7% on time and Thursday the weakest at 69.3%, 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 89,000 reported delay minutes.
- 40%National Airspace System
- 35%Late-arriving aircraft
- 23%Carrier
- 2%Extreme weather
- 0%Security
35% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 89,000 reported delay minutes here, that single category outweighs weather by 16 to one. The split is drawn from 88,918 reported delay minutes.
40% 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 36,000 minutes out of 89,000, against a national NAS share of 21%.
Cancellations sit at 1.81% against a national 1.89%, which is ordinary. Diversions add another 0.19%.
Connections and stage length
What a delay here actually costs
10.2% 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 69.2% on time across 4,817 flights, 5 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 5 points of difference.
The sample behind these figures is 4,815 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 BOS 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. February runs 84.6% on time and July 67.1%, a swing of 18 points. If the dates move at all, move them out of July before you think about anything else. 4,719 completed flights over 12 months sit behind that.
Common questions
SFO to BOS questions
How often is SFO to BOS delayed?
About one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 25.5% of the 4,815 flights in this analysis, against 22.7% nationally. Delayed flights are late by a little over an hour on average.
Which airline is most reliable on SFO to BOS?
United Airlines leads at 78.5% on time across 1,939 flights. JetBlue Airways is at the other end on 71.5%, a gap of 7 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 SFO to BOS?
The 5am–8am departure window is the strongest at 87.1% on time. The 11am–2pm window is the weakest at 65.7%, 21 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 July delays on SFO to BOS?
July is the weakest month at 67.1% on time, compared with 84.6% in February. Across the year that is 18 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
- BOS to SFO — the return legseparate record
- San Francisco International (SFO) delay statistics
- Boston Logan International (BOS) delay statistics
- Alaska Airlines on SFO to BOS80.3%
- United Airlines on SFO to BOS78.5%
- Delta Air Lines on SFO to BOS71.5%
- JetBlue Airways on SFO to BOS71.5%
- SFO to LAX, a related route70.9%
- DCA to BOS, a related route70.1%
- SFO to SEA, a related route72.3%
- Alaska Airlines on-time record80.3%
- United Airlines on-time record78.5%
- Delta Air Lines on-time record71.5%
- Why the first flight of the morning is statistically safest
- How often a connection fails at the major US hubs
Direction matters. SFO to BOS and BOS to SFO 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.