Route reliability record

BOS→SFO

Boston to San Francisco

Flights: 4,676
Period: July 2025 to June 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, 5 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 4,676 flights, of which United Airlines flew 1,867 at 76.3% on time.

United Airlines is the most reliable of the three carriers covered here at 76.3% on time across 1,867 flights.

On time

72.6%

Arrivals under 15 minutes late, of 4,604 completed flights

Avg delay

65 min

Across delayed arrivals only, not all flights

Cancelled

1.22%

National rate is 1.81%

Best carrier

United

76.3% on time across 1,867 flights

These figures cover 4,676 flights between July 2025 and June 2026. Beyond the headline rate, 9.5% 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.

On-time performance by carrier on BOS to SFO
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	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.

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 24 points, against 6 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,041 flights83.9%
8am–11am916 flights81.5%
11am–2pm380 flights76.4%
2pm–5pm678 flights69.3%
5pm–8pm952 flights60.0%
8pm–5am709 flights62.5%

Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 60.0% on time, against 83.9% 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 5am–8am window is the busiest, with 1,041 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 28 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.

Darker means more delays. Figures are on-time percentages.August best, June worst

June is the worst month at 56.5% on time, 28 points below August, the best at 84.4%. 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. June was the busiest month here, with 502 flights.

Across the week, Tuesday is the strongest day at 78.9% on time and Thursday the weakest at 67.8%. 11 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 82,000 reported delay minutes.

National Airspace System
39%
Late-arriving aircraft
36%
Carrier
23%
Extreme weather
2%
Security
0%

36% 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 82,000 reported delay minutes here, that single category outweighs weather by 20 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. The split is drawn from 81,903 reported delay minutes.

39% 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 32,000 minutes out of 82,000, against a national NAS share of 21%.

Cancellations sit at 1.22% against a national 1.81%, which is ordinary. Diversions add another 0.32%.

Connections and stage length

What a delay here actually costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.5% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum 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 76.9% on time across 4,674 flights, 4 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 4 points of difference.

The sample behind these figures is 4,676 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 June 56.5%, a swing of 28 points. If the dates move at all, move them out of June before you think about anything else. 4,604 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 four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 27.4% of the 4,676 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on BOS to SFO?

United Airlines leads at 76.3% on time across 1,867 flights. JetBlue Airways is at the other end on 70.5%, 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 83.9% on time. The 5pm–8pm window is the weakest at 60.0%, 24 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 84.4% in August. Across the year that is 28 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

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, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures