Route reliability record
BOI→SEA
Boise to Seattle
- Flights
- 3,820
- Period
- July 2025 to June 2026
- Distance
- 399 mi
- Carriers
- 2
This route earns a A+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 8 points better than the national rate of 77.6%. When something does go wrong the average delay runs about an hour. That rests on 3,820 flights, of which SkyWest Airlines flew 2,929 at 86.2% on time.
Set against the rest of the country, this route's record is 8 points better than the US average of 77.6%. That gap is worth roughly 81 fewer late arrivals for every thousand flights.
Key figures
On time
85.7%
Arrivals under 15 minutes late, of 3,802 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
0.39%
National rate is 1.81%
Best carrier
SkyWest
86.2% on time across 2,929 flights
These figures cover 3,820 flights between July 2025 and June 2026. The median arrival is 11 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
Which airline is most reliable on BOI to SEA
The two carriers here are closely matched: 2 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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SkyWest Airlines | 2,929 | 86.2% | 58 min | 0.27% | A+ |
| Alaska Airlines | 891 | 84.0% | 50 min | 0.79% | B+ |
No carrier stands out. SkyWest tops the table at 86.2%, 2 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 30 points, against 2 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,033 flights93.3%
- 8am–11am800 flights85.4%
- 11am–2pm410 flights88.5%
- 2pm–5pm743 flights83.0%
- 5pm–8pm718 flights80.0%
- 8pm–5am116 flights62.9%
Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 62.9% on time, against 93.3% 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 1,033 flights scheduled in it.
Across the year
When delays peak on this route
Twelve months, one bar each, drawn from the same 3,820 flights. The strip shows how much of this route's record is set by the calendar rather than by the operation.
August is the worst month at 81.7% on time, 11 points below February, the best at 92.8%. 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 369 flights.
Across the week, Saturday is the strongest day at 89.2% on time and Thursday the weakest at 80.1%. 9 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Carrier accounts for 53% of the 30,000 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.
- 53%Carrier
- 21%National Airspace System
- 14%Late-arriving aircraft
- 13%Extreme weather
- 0%Security
Extreme weather accounts for 13% of delay minutes, well above the single-digit share typical across the system. Weather delays are lumpy: they arrive as whole bad days rather than as a steady drag, so the monthly strip above is the more useful view of the risk. The national share is 6%, so this operation carries roughly 2.1 times the usual weather exposure. The split is drawn from 30,399 reported delay minutes.
The largest share of delay minutes, 53%, 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 16,000 of the 30,000 delay minutes reported here.
Cancellations are rare at 0.39%, 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 actually 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 5am–8am window matters as much as it does.
The return leg runs 85.8% on time across 3,972 flights, within half a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
The sample behind these figures is 3,820 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: avoid the 8pm–5am departure. It runs 62.9% on time against 93.3% for the 5am–8am slot, and that 30 points is the largest single thing you control here. SkyWest Airlines is the strongest operator if the fares are close. 3,802 completed flights over 12 months sit behind that.
Common questions
BOI to SEA questions
How often is BOI to SEA delayed?
About one flight in seven arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 14.3% of the 3,820 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on BOI to SEA?
SkyWest Airlines leads at 86.2% on time across 2,929 flights. Alaska Airlines is at the other end on 84.0%, a gap of 2 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 BOI to SEA?
The 5am–8am departure window is the strongest at 93.3% on time. The 8pm–5am window is the weakest at 62.9%, 30 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 August delays on BOI to SEA?
August is the weakest month at 81.7% on time, compared with 92.8% in February. Across the year that is 11 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- SEA to BOI — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- SkyWest Airlines on-time record86.2%
- Alaska Airlines on-time record84.0%
- The best time of day to fly, according to 7.04 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. BOI to SEA and SEA to BOI 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.