Carrier route record

ASBOS→SFO

Alaska Airlines · Boston to San Francisco

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 BOS to SFO draws a D+. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 234 flights. The strongest carrier on the route with a full sample, 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

61.6%

Arrivals under 15 minutes late, of 229 completed flights

Avg delay

66 min

Across delayed arrivals only, not all flights

Cancelled

0.43%

National rate is 1.81%

Whole route

72.6%

Every carrier on BOS to SFO, 4,676 flights

These figures cover 234 flights between July 2025 and June 2026. Beyond the headline rate, 14.8% 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 BOS to SFO

Alaska flew 234 of the 4,676 flights on BOS to SFO, about 5% of it. Its 61.6% on time is 11 points worse than the route as a whole, which runs 72.6%. Ranked by on-time rate it is last of five carriers on the route, where the range runs from Southwest at 100.0% to Alaska at 61.6%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

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 Airlines (this page)thin 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

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

5am–8am50 flights80.0%
8am–11am—
11am–2pm—
2pm–5pm—
5pm–8pm68 flights51.6%
8pm–5am116 flights59.1%

Scale runs 45% to 85%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 51.6% on time, against 80.0% 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 8pm–5am window is the busiest, with 116 flights scheduled in it.

Across the year

Alaska on BOS to SFO through the year

Jul–Sep 2025141 flights66.0%
Oct–Dec 202587 flights56.6%
Jan–Mar 20266 flights—

Scale runs 50% to 70%. 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 61.6% on time across 234 flights.

Split by quarter, Alaska on BOS to SFO 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 61.6% annual figure is the one to use.

Across the week, Tuesday is the strongest day at 75.0% on time and Thursday the weakest at 45.2%. 30 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. Late-arriving aircraft accounts for 71% of the 5,829 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.

Late-arriving aircraft
71%
National Airspace System
15%
Carrier
12%
Extreme weather
1%
Security
0%

71% 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 5,829 reported delay minutes here, that single category outweighs weather by 69 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 5,829 reported delay minutes.

The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 80.0% on time here.

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

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 14.8% 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 77.3% on time across 234 flights, 16 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 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 BOS to SFO

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 61.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 229 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