Route reliability record

BOI→DEN

Boise to Denver

Flights: 3,035
Period: July 2025 to June 2026
Distance: 649 mi
Carriers: 4

This route lands a B+, 3 points better than the national rate of 77.6%. About one flight in five arrive 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 3,035 flights, of which SkyWest Airlines flew 871 at 85.8% on time.

SkyWest Airlines is the most reliable of the three carriers covered here at 85.8% on time across 871 flights.

On time

80.9%

Arrivals under 15 minutes late, of 3,019 completed flights

Avg delay

77 min

Across delayed arrivals only, not all flights

Cancelled

0.20%

National rate is 1.81%

Best carrier

SkyWest

85.8% on time across 871 flights

These figures cover 3,035 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

Which airline is most reliable on BOI to DEN

The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 85.8% of the time; Southwest Airlines manages 77.8%. Sample sizes sit next to every figure, because a two-point gap across 1,092 flights means less than a ten-point one.

On-time performance by carrier on BOI to DEN
Airline	Flights	On time	Avg delay	Cancelled	Grade
SkyWest Airlines	871	85.8%	86 min	0.00%	A+
Frontier Airlinesthin sample	126	80.2%	141 min	0.00%	B+
United Airlines	946	80.1%	89 min	0.53%	B+
Southwest Airlines	1,092	77.8%	56 min	0.09%	B+

SkyWest leads Southwest by 8 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 29 points, against 8 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am951 flights92.9%
8am–11am631 flights88.3%
11am–2pm377 flights82.9%
2pm–5pm641 flights65.8%
5pm–8pm434 flights64.3%
8pm–5am1 flights—

Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 64.3% on time, against 92.9% 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 951 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 20 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.

Darker means more delays. Figures are on-time percentages.January best, July worst

July is the worst month at 70.0% on time, 20 points below January, the best at 90.2%. 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. May was the busiest month here, with 261 flights.

Across the week, Saturday is the strongest day at 85.6% on time and Friday the weakest at 72.6%. 13 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 44,000 reported delay minutes.

National Airspace System
35%
Carrier
35%
Late-arriving aircraft
27%
Extreme weather
4%

The largest share of delay minutes, 35%, 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 15,000 of the 44,000 delay minutes reported here. The split is drawn from 44,187 reported delay minutes.

35% 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 15,000 minutes out of 44,000, against a national NAS share of 21%.

Cancellations are rare at 0.20%, 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

6.8% 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 are the a little over an hour kind, which a normal layover absorbs.

The 649 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.

The return leg is a different operation and performs like one: it runs 76.3% on time across 3,039 flights, 5 points below 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 5 points of difference.

The sample behind these figures is 3,035 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: the calendar is the biggest lever here, not the carrier or the hour. January runs 90.2% on time and July 70.0%, a swing of 20 points. If the dates move at all, move them out of July before you think about anything else. 3,019 completed flights over 12 months sit behind that.

Common questions

BOI to DEN questions

How often is BOI to DEN delayed?

About one flight in five arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 19.1% of the 3,035 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on BOI to DEN?

SkyWest Airlines leads at 85.8% on time across 871 flights. Southwest Airlines is at the other end on 77.8%, a gap of 8 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 DEN?

The 5am–8am departure window is the strongest at 92.9% on time. The 5pm–8pm window is the weakest at 64.3%, 29 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 BOI to DEN?

July is the weakest month at 70.0% on time, compared with 90.2% in January. Across the year that is 20 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. BOI to DEN and DEN 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.

Key figures