Route reliability record
BOI→SEA
Boise to Seattle
- Flights
- 3,730
- Period
- September 2025 to August 2026
- Distance
- 399 mi
- Carriers
- 2
This route earns a B+. 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 77.3%. When something does go wrong the average delay runs about an hour. That rests on 3,730 BOI to SEA flights, of which SkyWest Airlines flew 2,754 at 85.9% on time.
Best time to fly BOI to SEA: a 5am–8am departure, ideally on a Saturday. Flights in that window arrived on time 93.2% of the time and Saturday flights 89.3%, against 84.9% for the route overall.
Set against the rest of the country, this route's record is 8 points better than the US average of 77.3%. That gap is worth roughly 76 fewer late arrivals for every thousand flights.
Key figures
On time
84.9%
Arrivals under 15 minutes late, of 3,712 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
0.40%
National rate is 1.89%
Best carrier
SkyWest
85.9% on time across 2,754 flights
These figures cover 3,730 flights between September 2025 and August 2026. The median arrival is 10 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.
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Carrier by carrier
Which airline is most reliable on BOI to SEA
The two 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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SkyWest Airlines | 2,754 | 85.9% | 61 min | 0.29% | A+ |
| Alaska Airlines | 976 | 82.2% | 44 min | 0.72% | B+ |
No carrier stands out. SkyWest tops the table at 85.9%, 4 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Flights on BOI to SEA
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly Boise to Seattle
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. BOI → SEABoise to Seattle | SkyWest Airlines | 85.7% | 85.9% | 0.29% | 5am–8am, Sat | OO 3775 05:40 |
| 2. BOI → SEABoise to Seattle | Alaska Airlines | 81.6% | 82.2% | 0.72% | 5am–8am, Sat | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 31 points, against 4 points between the best and worst carrier.
- 5am–8am972 flights93.2%
- 8am–11am826 flights84.4%
- 11am–2pm401 flights88.9%
- 2pm–5pm699 flights82.6%
- 5pm–8pm722 flights78.1%
- 8pm–5am110 flights61.8%
Scale runs 55% to 100%.
The 8pm–5am window is where this operation falls apart: 61.8% on time, against 93.2% 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 972 flights scheduled in it.
Explore
Filter BOI to SEA by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On BOI to SEA, the best departure window is 5am–8am at 93.2% on time and the worst is 8pm–5am at 61.8%, a wide gap of 31.4 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am93.2%
- 8–11am84.4%
- 11am–2pm88.9%
- 2–5pm82.6%
- 5–8pm78.1%
- 8pm–5am61.8%
best all US flightsScale 55% to 100%.
Across the year
When delays peak on this route
This route's year swings by 15 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
August is the worst month at 77.9% on time, 15 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 89.3% on time and Thursday the weakest at 78.5%, a spread of 11 points.
Delay causes
Why this route gets delayed
Carrier accounts for 53% of the 31,000 delay minutes carriers reported here, and the remaining four split what is left.
- 53%Carrier
- 23%National Airspace System
- 13%Extreme weather
- 11%Late-arriving aircraft
- 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 2.2 times the usual weather exposure. The split is drawn from 31,060 reported delay minutes.
The largest share of delay minutes, 53%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 16,000 of the 31,000 delay minutes reported here.
Cancellations are rare at 0.40%, below the national 1.89% 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 4.1% land an hour or more behind schedule, against 8.3% 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 86.3% on time across 3,829 flights, within about 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 3,730 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.
Work out the risk of missing a connection in SEA after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 92.8% on time and August 77.9%, a swing of 15 points. If the dates move at all, move them out of August before you think about anything else. 3,712 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 arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 15.1% of the 3,730 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on BOI to SEA?
SkyWest Airlines leads at 85.9% on time across 2,754 flights. Alaska Airlines is at the other end on 82.2%, a gap of 4 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 93.2% on time. The 8pm–5am window is the weakest at 61.8%, 31 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 77.9% on time, compared with 92.8% in February. Across the year that is 15 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 BOI to SEA85.9%
- Alaska Airlines on BOI to SEA82.2%
- BOI to DEN, a related route81.7%
- LAX to SEA, a related route85.0%
- BOI to PHX, a related route84.2%
- SkyWest Airlines on-time record85.9%
- Alaska Airlines on-time record82.2%
- The best time of day to fly, according to 7.05 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.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.