Carrier route record

F9DEN→BOI

Frontier Airlines · Denver to Boise

Flights: 126
Period: July 2025 to June 2026
Share of route: 4%
Carriers: 4

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

Frontier on DEN to BOI lands a B+, about a point 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 about 40 minutes on average. That is a workable record, not a spotless one. That rests on 126 flights. The strongest carrier on the route with a full sample, United Airlines, flew 946 at 79.2% on time.

United Airlines is the most reliable of the three carriers covered here at 79.2% on time across 946 flights.

On time

78.6%

Arrivals under 15 minutes late, of 126 completed flights

Avg delay

39 min

Across delayed arrivals only, not all flights

Cancelled

0.00%

National rate is 1.81%

Whole route

76.3%

Every carrier on DEN to BOI, 3,039 flights

These figures cover 126 flights between July 2025 and June 2026. The median arrival is 2 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

Frontier against every carrier on DEN to BOI

Frontier flew 126 of the 3,039 flights on DEN to BOI, about 4% of it. Its 78.6% on time is 2 points better than the route as a whole, which runs 76.3%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from United at 79.2% to Southwest at 71.5%.

The choice of carrier is not cosmetic here. United Airlines arrives on time 79.2% of the time; Southwest Airlines manages 71.5%. Sample sizes sit next to every figure, because a two-point gap across 1,093 flights means less than a ten-point one.

On-time performance by carrier on DEN to BOI
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	946	79.2%	57 min	0.32%	B+
SkyWest Airlines	874	78.7%	71 min	0.11%	B+
Frontier Airlines (this page)thin sample	126	78.6%	39 min	0.00%	B+
Southwest Airlines	1,093	71.5%	46 min	0.18%	C+

United leads Southwest by 8 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Departure window

When Frontier runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 126 flights.

There are not enough flights in each departure window to split Frontier's DEN to BOI record by time of day without the percentages moving on noise. The headline rate of 78.6% is the reliable figure here.

Across the year

Frontier on DEN to BOI through the year

Jul–Sep 202530 flights70.0%
Oct–Dec 202536 flights75.0%
Jan–Mar 202632 flights93.8%
Apr–Jun 202628 flights—

Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 78.6% on time across 126 flights.

Frontier on DEN to BOI did not run the same all year. Its best quarter was Jan–Mar 2026 at 93.8% on time and its weakest Jul–Sep 2025 at 70.0%, a swing of 24 points on roughly 42 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.

Across the week, Thursday is the strongest day at 81.8% on time and Sunday the weakest at 70.2%. 12 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Frontier runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 42% of the 1,058 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
42%
Carrier
34%
National Airspace System
24%

42% 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 1,058 reported delay minutes here, that single category outweighs weather by 42 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 1,058 reported delay minutes.

The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 77.9% on time here.

Cancellations are rare at 0.00%, below the national 1.81% and low enough to earn the plus on the grade. Almost no flights are 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 2.4% 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.

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 runs 80.2% on time across 126 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

One caution: this is a thin sample. 126 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 Frontier on DEN to BOI

Put together: treat all of this as provisional. 126 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 78.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 126 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