Carrier route record

ASSAN→DEN

Alaska Airlines · San Diego to Denver

Flights: 433
Period: July 2025 to June 2026
Share of route: 7%
Carriers: 5

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

Alaska on SAN to DEN lands a B, 6 points better than the national rate of 77.6%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 433 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

83.4%

Arrivals under 15 minutes late, of 428 completed flights

Avg delay

57 min

Across delayed arrivals only, not all flights

Cancelled

1.15%

National rate is 1.81%

Whole route

79.2%

Every carrier on SAN to DEN, 5,947 flights

These figures cover 433 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

Alaska against every carrier on SAN to DEN

Alaska flew 433 of the 5,947 flights on SAN to DEN, about 7% of it. Its 83.4% on time is 4 points better than the route as a whole, which runs 79.2%. Ranked by on-time rate it is number two 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 (this page)	433	83.4%	57 min	1.15%	B
Frontier Airlines	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.

Departure window

When Alaska runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 31 points, against 13 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am21 flights—
8am–11am173 flights90.0%
11am–2pm35 flights97.1%
2pm–5pm125 flights66.1%
5pm–8pm—
8pm–5am79 flights87.3%

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

The best window here is not the first bank but the 11am–2pm slot at 97.1% on time, ahead of 2pm–5pm at 66.1%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 8am–11am window is the busiest, with 173 flights scheduled in it.

Across the year

Alaska on SAN to DEN through the year

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

December is the weak month at 40.0% on time, against 95.3% in June. 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 77 flights.

Across the week, Saturday is the strongest day at 87.5% on time and Sunday the weakest at 75.4%. 12 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Alaska runs late on this route

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 4,052 reported delay minutes.

National Airspace System
35%
Late-arriving aircraft
34%
Carrier
27%
Extreme weather
4%

34% 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 4,052 reported delay minutes here, that single category outweighs weather by 8 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 4,052 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 1,415 minutes out of 4,052, against a national NAS share of 21%.

Cancellations sit at 1.15% against a national 1.81%, which is ordinary. Diversions add another 0.00%.

Connections and stage length

What a delay here costs

Badly late arrivals are rare here: only 4.4% 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 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 82.9% on time across 433 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.

One caution: this is a thin sample. 433 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 Alaska on SAN to DEN

Put together: treat all of this as provisional. 433 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 83.4% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 428 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