Carrier route record
WNSAN→DEN
Southwest Airlines · San Diego to Denver
- Flights
- 2,387
- 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 SAN to DEN sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 5 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 2,387 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.
Key figures
On time
72.4%
Arrivals under 15 minutes late, of 2,358 completed flights
Avg delay
57 min
Across delayed arrivals only, not all flights
Cancelled
0.75%
National rate is 1.81%
Whole route
79.2%
Every carrier on SAN to DEN, 5,947 flights
These figures cover 2,387 flights between July 2025 and June 2026. Beyond the headline rate, 8.7% 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 SAN to DEN
Southwest flew 2,387 of the 5,947 flights on SAN to DEN, about 40% of it. Its 72.4% on time is 7 points worse than the route as a whole, which runs 79.2%. Ranked by on-time rate it is last 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 three carriers here are closely matched: 4 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.
| 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 | 704 | 81.6% | 79 min | 1.28% | B |
| SkyWest Airlinesthin sample | 342 | 79.2% | 45 min | 1.46% | B |
| Southwest Airlines (this page) | 2,387 | 72.4% | 57 min | 0.75% | C+ |
No carrier stands out. United tops the table at 85.4%, 4 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 37 points, against 4 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am430 flights89.0%
- 8am–11am445 flights89.6%
- 11am–2pm479 flights68.2%
- 2pm–5pm503 flights53.0%
- 5pm–8pm378 flights64.7%
- 8pm–5am152 flights71.2%
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 89.6% of the time, against 53.0% for the afternoon window. That is 37 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 503 flights scheduled in it.
Across the year
Southwest on SAN to DEN through the year
June is the worst month at 54.2% on time, 32 points below January, the best at 86.0%. 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, Saturday is the strongest day at 84.0% on time and Friday the weakest at 62.8%. 21 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 49% of the 37,000 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.
- 49%Late-arriving aircraft
- 29%National Airspace System
- 20%Carrier
- 2%Extreme weather
- 0%Security
49% 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 37,000 reported delay minutes here, that single category outweighs weather by 32 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 36,969 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 89.6% on time here.
Cancellations are rare at 0.75%, 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
8.7% 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 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 69.5% on time across 2,389 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 2,387 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 SAN to DEN
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 86.0% on time and June 54.2%, a swing of 32 points. If the dates move at all, move them out of June before you think about anything else. 2,358 completed flights over 12 months sit behind that.
Related
Where to go next
- SAN to DEN, every carrier
- Southwest on DEN to SAN, the return leg
- United Airlines on SAN to DEN85.4%
- Alaska Airlines on SAN to DEN83.4%
- Frontier Airlines on SAN to DEN81.6%
- SkyWest Airlines on SAN to DEN79.2%
- Southwest Airlines network-wide record
- San Diego International (SAN) delay statistics
- Denver International (DEN) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.