Carrier route record

ASBOS→SEA

Alaska Airlines · Boston to Seattle

Flights: 1,208
Period: July 2025 to June 2026
Share of route: 49%
Carriers: 3

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

Alaska on BOS to SEA sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 7 points worse than the national rate of 77.6%. The late ones land about 50 minutes behind schedule. That rests on 1,208 flights, with a median arrival 2 minutes early.

The national on-time rate over the same period is 77.6%, so Alaska on BOS to SEA runs 7 points behind the country as a whole. Across a thousand flights that is about 71 extra late arrivals.

On time

70.5%

Arrivals under 15 minutes late, of 1,186 completed flights

Avg delay

50 min

Across delayed arrivals only, not all flights

Cancelled

1.16%

National rate is 1.81%

Whole route

71.4%

Every carrier on BOS to SEA, 2,461 flights

These figures cover 1,208 flights between July 2025 and June 2026. The median arrival is 2 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.

Carrier by carrier

Alaska against every carrier on BOS to SEA

Alaska flew 1,208 of the 2,461 flights on BOS to SEA, about 49% of it. Its 70.5% on time is about level with the route as a whole at 71.4%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from JetBlue at 75.6% to Alaska at 70.5%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.

On-time performance by carrier on BOS to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
JetBlue Airwaysthin sample	247	75.6%	72 min	0.40%	B+
Delta Air Lines	1,006	71.6%	55 min	1.59%	C
Alaska Airlines (this page)	1,208	70.5%	50 min	1.16%	C

Flight by flight

Alaska flight numbers on BOS to SEA

AS 45907:2072.1% · 364 flights

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 21 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am364 flights72.1%
8am–11am323 flights76.5%
11am–2pm—
2pm–5pm159 flights80.4%
5pm–8pm361 flights59.1%
8pm–5am1 flights—

Scale runs 50% to 85%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 59.1% on time, against 80.4% for the 2pm–5pm 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 364 flights scheduled in it.

Across the year

Alaska on BOS to SEA through the year

Darker means more delays. Figures are on-time percentages.September best, December worst

December is the weak month at 33.3% on time, against 82.4% in September. 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. May was the busiest month here, with 124 flights.

Across the week, Monday is the strongest day at 76.2% on time and Thursday the weakest at 61.2%. 15 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 45% of the 17,000 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
45%
National Airspace System
37%
Carrier
15%
Extreme weather
3%
Security
0%

45% 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 17,000 reported delay minutes here, that single category outweighs weather by 17 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 17,470 reported delay minutes.

37% 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 6,536 minutes out of 17,000, against a national NAS share of 21%.

Cancellations sit at 1.16% against a national 1.81%, which is ordinary. Diversions add another 0.66%.

Connections and stage length

What a delay here costs

6.7% 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 50 minutes, which a normal layover absorbs.

At 2,496 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 73.7% on time across 1,207 flights, 3 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 3 points of difference.

The sample behind these figures is 1,208 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 Alaska on BOS to SEA

Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 82.4% on time and December 33.3%, a swing of 49 points. If the dates move at all, move them out of December before you think about anything else. 1,186 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