Carrier route record

ASSEA→BOI

Alaska Airlines · Seattle to Boise

Flights: 891
Period: July 2025 to June 2026
Share of route: 22%
Carriers: 2

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

Alaska on SEA to BOI lands a B+, 3 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 45 minutes on average. That is a workable record, not a spotless one. That rests on 891 flights, with a median arrival 7 minutes early.

The US average over the same twelve months is 77.6%, so there is little to separate Alaska on SEA to BOI from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

80.8%

Arrivals under 15 minutes late, of 887 completed flights

Avg delay

43 min

Across delayed arrivals only, not all flights

Cancelled

0.45%

National rate is 1.81%

Whole route

85.8%

Every carrier on SEA to BOI, 3,972 flights

These figures cover 891 flights between July 2025 and June 2026. The median arrival is 7 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 SEA to BOI

Alaska flew 891 of the 3,972 flights on SEA to BOI, about 22% of it. Its 80.8% on time is 5 points worse than the route as a whole, which runs 85.8%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from SkyWest at 87.2% to Alaska at 80.8%.

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 SEA to BOI
Airline	Flights	On time	Avg delay	Cancelled	Grade
SkyWest Airlines	3,081	87.2%	52 min	0.19%	A+
Alaska Airlines (this page)	891	80.8%	43 min	0.45%	B+

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 16 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–8am22 flights—
8am–11am97 flights91.6%
11am–2pm364 flights83.5%
2pm–5pm—
5pm–8pm2 flights—
8pm–5am406 flights75.5%

Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.

Book the morning departure. Flights leaving between 8am–11am arrive on time 91.6% of the time, against 75.5% for the overnight window. That is 16 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8pm–5am window is the busiest, with 406 flights scheduled in it.

Across the year

Alaska on SEA to BOI through the year

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

August is the worst month at 64.5% on time, 25 points below February, the best at 89.6%. 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. March was the busiest month here, with 97 flights.

Across the week, Wednesday is the strongest day at 86.5% on time and Friday the weakest at 73.4%. 13 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 51% of the 7,299 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
51%
Carrier
40%
National Airspace System
8%
Extreme weather
1%

51% 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 7,299 reported delay minutes here, that single category outweighs weather by 51 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 7,299 reported delay minutes.

The largest share of delay minutes, 40%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 2,940 of the 7,299 delay minutes reported here.

Cancellations are rare at 0.45%, 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

Badly late arrivals are rare here: only 3.8% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

At 399 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 8am–11am window matters as much as it does.

The return leg is a different operation and performs like one: it runs 84.0% on time across 891 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.

One caution: this is a thin sample. 891 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 SEA to BOI

Put together: treat all of this as provisional. 891 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 80.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 887 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