Route reliability record
SEA→BOI
Seattle to Boise
- Flights
- 3,972
- 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 50 minutes. That rests on 3,972 flights, of which SkyWest Airlines flew 3,081 at 87.2% 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 82 fewer late arrivals for every thousand flights.
Key figures
On time
85.8%
Arrivals under 15 minutes late, of 3,961 completed flights
Avg delay
49 min
Across delayed arrivals only, not all flights
Cancelled
0.25%
National rate is 1.81%
Best carrier
SkyWest
87.2% on time across 3,081 flights
These figures cover 3,972 flights between July 2025 and June 2026. The median arrival is 8 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 SEA to BOI
The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 87.2% of the time; Alaska Airlines manages 80.8%. Sample sizes sit next to every figure, because a two-point gap across 891 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SkyWest Airlines | 3,081 | 87.2% | 52 min | 0.19% | A+ |
| Alaska Airlines | 891 | 80.8% | 43 min | 0.45% | B+ |
SkyWest leads Alaska by 6 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
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 12 points, against 6 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am416 flights92.1%
- 8am–11am694 flights88.7%
- 11am–2pm859 flights85.7%
- 2pm–5pm516 flights85.2%
- 5pm–8pm711 flights85.9%
- 8pm–5am776 flights80.1%
Scale runs 70% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 92.1% of the time, against 80.1% for the overnight window. That is 12 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 859 flights scheduled in it.
Across the year
When delays peak on this route
Twelve months, one bar each, drawn from the same 3,972 flights. The strip shows how much of this route's record is set by the calendar rather than by the operation.
July is the worst month at 79.9% on time, 12 points below October, the best at 91.6%. 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. July was the busiest month here, with 394 flights.
Across the week, Saturday is the strongest day at 89.7% on time and Sunday the weakest at 82.4%. 7 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 50% of the 28,000 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.
- 50%Carrier
- 22%Late-arriving aircraft
- 15%Extreme weather
- 13%National Airspace System
- 0%Security
Extreme weather accounts for 15% 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 2.5 times the usual weather exposure. The split is drawn from 27,707 reported delay minutes.
The largest share of delay minutes, 50%, 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 14,000 of the 28,000 delay minutes reported here.
Cancellations are rare at 0.25%, 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 3.6% 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 85.7% on time across 3,820 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 3,972 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 80.1% on time against 92.1% for the 5am–8am slot, and that 12 points is the largest single thing you control here. SkyWest Airlines is the strongest operator if the fares are close. 3,961 completed flights over 12 months sit behind that.
Common questions
SEA to BOI questions
How often is SEA to BOI 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 14.2% of the 3,972 flights in this analysis, against 22.4% nationally. Delayed flights are late by about 50 minutes on average.
Which airline is most reliable on SEA to BOI?
SkyWest Airlines leads at 87.2% on time across 3,081 flights. Alaska Airlines is at the other end on 80.8%, a gap of 6 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 SEA to BOI?
The 5am–8am departure window is the strongest at 92.1% on time. The 8pm–5am window is the weakest at 80.1%, 12 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 July delays on SEA to BOI?
July is the weakest month at 79.9% on time, compared with 91.6% in October. Across the year that is 12 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
- BOI to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- SkyWest Airlines on-time record87.2%
- Alaska Airlines on-time record80.8%
- 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. SEA to BOI and BOI to SEA 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.