Carrier route record

F9SAN→DEN

Frontier Airlines · San Diego to Denver

Flights: 704
Period: July 2025 to June 2026
Share of route: 12%
Carriers: 5

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

Frontier on SAN to DEN lands a B, 4 points better than the national rate of 77.6%. Roughly one flight in five arrives 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 704 flights. The strongest carrier on the route with a full sample, United Airlines, flew 2,081 at 85.4% on time.

United Airlines is the most reliable of the three carriers covered here at 85.4% on time across 2,081 flights.

On time

81.6%

Arrivals under 15 minutes late, of 694 completed flights

Avg delay

79 min

Across delayed arrivals only, not all flights

Cancelled

1.28%

National rate is 1.81%

Whole route

79.2%

Every carrier on SAN to DEN, 5,947 flights

These figures cover 704 flights between July 2025 and June 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.

Carrier by carrier

Frontier against every carrier on SAN to DEN

Frontier flew 704 of the 5,947 flights on SAN to DEN, about 12% of it. Its 81.6% on time is 2 points better than the route as a whole, which runs 79.2%. Ranked by on-time rate it is number three of five carriers on the route, where the range runs from United at 85.4% to Southwest at 72.4%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. United Airlines arrives on time 85.4% of the time; Southwest Airlines manages 72.4%. Sample sizes sit next to every figure, because a two-point gap across 2,387 flights means less than a ten-point one.

On-time performance by carrier on SAN to DEN
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	2,081	85.4%	65 min	0.77%	A+
Alaska Airlines	433	83.4%	57 min	1.15%	B
Frontier Airlines (this page)	704	81.6%	79 min	1.28%	B
SkyWest Airlinesthin sample	342	79.2%	45 min	1.46%	B
Southwest Airlines	2,387	72.4%	57 min	0.75%	C+

The spread between United and Southwest is 13 points, wide enough that it should decide the booking. On a hundred trips that is 13 more arrivals inside the on-time window.

Flight by flight

Frontier flight numbers on SAN to DEN

F9 281806:2584.4% · 362 flights

Departure window

When Frontier runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 25 points, against 13 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am358 flights84.2%
8am–11am108 flights82.1%
11am–2pm119 flights80.5%
2pm–5pm35 flights58.8%
5pm–8pm23 flights—
8pm–5am61 flights79.7%

Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 84.2% of the time, against 58.8% for the afternoon window. That is 25 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 358 flights scheduled in it.

Across the year

Frontier on SAN to DEN through the year

Darker means more delays. Figures are on-time percentages.May best, December worst

December is the weak month at 68.5% on time, against 94.4% in May. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. March was the busiest month here, with 68 flights.

Across the week, Wednesday is the strongest day at 87.5% on time and Friday the weakest at 75.7%. 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 50% of the 10,000 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.

Late-arriving aircraft
50%
Carrier
31%
National Airspace System
17%
Extreme weather
3%

50% 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 10,000 reported delay minutes here, that single category outweighs weather by 19 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 10,123 reported delay minutes.

The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 84.2% on time here.

Cancellations sit at 1.28% against a national 1.81%, which is ordinary. Diversions add another 0.14%.

Connections and stage length

What a delay here costs

7.2% 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 last a little over an hour, which a normal layover absorbs.

The 853 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 79.6% on time across 703 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. 704 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 SAN to DEN

Put together: treat all of this as provisional. 704 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 81.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 694 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