Carrier route record

WNDEN→SAN

Southwest Airlines · Denver to San Diego

Flights: 2,389
Period: July 2025 to June 2026
Share of route: 40%
Carriers: 5

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

Southwest on DEN to SAN sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 8 points worse than the national rate of 77.6%. The late ones land about 55 minutes behind schedule. That rests on 2,389 flights. The strongest carrier on the route with a full sample, Alaska Airlines, flew 433 at 82.9% on time.

Alaska Airlines is the most reliable of the three carriers covered here at 82.9% on time across 433 flights.

On time

69.5%

Arrivals under 15 minutes late, of 2,366 completed flights

Avg delay

55 min

Across delayed arrivals only, not all flights

Cancelled

0.63%

National rate is 1.81%

Whole route

75.6%

Every carrier on DEN to SAN, 5,949 flights

These figures cover 2,389 flights between July 2025 and June 2026. Beyond the headline rate, 8.9% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

Carrier by carrier

Southwest against every carrier on DEN to SAN

Southwest flew 2,389 of the 5,949 flights on DEN to SAN, about 40% of it. Its 69.5% on time is 6 points worse than the route as a whole, which runs 75.6%. Ranked by on-time rate it is last of five carriers on the route, where the range runs from Alaska at 82.9% to Southwest at 69.5%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The three carriers here are closely matched: 3 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

On-time performance by carrier on DEN to SAN
Airline	Flights	On time	Avg delay	Cancelled	Grade
Alaska Airlines	433	82.9%	56 min	1.15%	B
United Airlines	2,081	79.8%	59 min	0.48%	B+
Frontier Airlines	703	79.6%	63 min	0.85%	B+
SkyWest Airlinesthin sample	343	75.0%	40 min	0.87%	B+
Southwest Airlines (this page)	2,389	69.5%	55 min	0.63%	C+

No carrier stands out. Alaska tops the table at 82.9%, 3 points clear of the bottom, which is inside the range this kind of sample moves year to year.

Departure window

When Southwest runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 42 points, against 3 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am359 flights93.8%
8am–11am489 flights82.1%
11am–2pm344 flights69.8%
2pm–5pm388 flights66.1%
5pm–8pm374 flights51.9%
8pm–5am435 flights52.8%

Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 51.9% on time, against 93.8% 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 8am–11am window is the busiest, with 489 flights scheduled in it.

Across the year

Southwest on DEN to SAN through the year

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

June is the worst month at 53.7% on time, 30 points below January, the best at 83.9%. 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. December was the busiest month here, with 221 flights.

Across the week, Tuesday is the strongest day at 75.2% on time and Thursday the weakest at 62.5%. 13 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Southwest runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 51% of the 40,000 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
51%
Carrier
29%
National Airspace System
18%
Extreme weather
1%
Security
0%

51% 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 40,000 reported delay minutes here, that single category outweighs weather by 44 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 39,507 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 93.8% on time here.

Cancellations are rare at 0.63%, 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 costs

8.9% 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 about 55 minutes, 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 72.4% on time across 2,387 flights, within 3 points 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 2,389 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 Southwest on DEN to SAN

Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 83.9% on time and June 53.7%, a swing of 30 points. If the dates move at all, move them out of June before you think about anything else. 2,366 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