Carrier route record

ASSFO→BOS

Alaska Airlines · San Francisco to Boston

Flights: 234
Period: July 2025 to June 2026
Share of route: 5%
Carriers: 5

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Alaska Airlines.

Alaska on SFO to BOS lands a B+, level with the national rate of 77.6%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 234 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,866 at 79.1% on time.

United Airlines is the most reliable of the three carriers covered here at 79.1% on time across 1,866 flights.

On time

77.3%

Arrivals under 15 minutes late, of 233 completed flights

Avg delay

57 min

Across delayed arrivals only, not all flights

Cancelled

0.43%

National rate is 1.81%

Whole route

76.9%

Every carrier on SFO to BOS, 4,674 flights

These figures cover 234 flights between July 2025 and June 2026. Beyond the headline rate, 8.2% 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

Alaska against every carrier on SFO to BOS

Alaska flew 234 of the 4,674 flights on SFO to BOS, about 5% of it. Its 77.3% on time is about level with the route as a whole at 76.9%. Ranked by on-time rate it is number two of five carriers on the route, where the range runs from United at 79.1% to Southwest at 0.0%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The three carriers here are closely matched: 4 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 SFO to BOS
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,866	79.1%	73 min	1.02%	B
Alaska Airlines (this page)thin sample	234	77.3%	57 min	0.43%	B+
JetBlue Airways	1,674	75.4%	76 min	1.79%	B
Delta Air Lines	899	75.1%	73 min	1.45%	B
Southwest Airlinesthin sample	1	0.0%	49 min	0.00%	F+

No carrier stands out. United tops the table at 79.1%, 4 points clear of the bottom, which is inside the range this kind of sample moves year to year.

Departure window

When Alaska runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 28 points, against 4 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am185 flights83.2%
8am–11am—
11am–2pm—
2pm–5pm—
5pm–8pm—
8pm–5am49 flights55.1%

Scale runs 45% to 90%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 55.1% on time, against 83.2% 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 185 flights scheduled in it.

Across the year

Alaska on SFO to BOS through the year

Jul–Sep 2025141 flights75.2%
Oct–Dec 202587 flights82.6%
Jan–Mar 20266 flights—

Scale runs 65% to 90%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 77.3% on time across 234 flights.

Split by quarter, Alaska on SFO to BOS logged 141 flights in Jul–Sep 2025, 87 flights in Oct–Dec 2025 and 6 flights in Jan–Mar 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 77.3% annual figure is the one to use.

Across the week, Saturday is the strongest day at 90.6% on time and Thursday the weakest at 63.6%. 27 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Alaska runs late on this route

One category carries most of the weight here. National Airspace System accounts for 51% of the 3,009 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.

National Airspace System
51%
Carrier
32%
Late-arriving aircraft
15%
Extreme weather
2%

51% 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 1,549 minutes out of 3,009, against a national NAS share of 21%. The split is drawn from 3,009 reported delay minutes.

Cancellations are rare at 0.43%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.

Connections and stage length

What a delay here costs

8.2% 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 61.6% on time across 234 flights, 16 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 16 points of difference.

One caution: this is a thin sample. 234 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 Alaska on SFO to BOS

Put together: treat all of this as provisional. 234 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 77.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 233 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures