Carrier route record
UASAN→DEN
United Airlines · San Diego to Denver
- Flights
- 2,081
- Period
- July 2025 to June 2026
- Share of route
- 35%
- Carriers
- 5
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.
United on SAN to DEN earns an A+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 8 points better than the national rate of 77.6%. When something does go wrong the average delay runs about an hour. That rests on 2,081 flights. The strongest carrier on the route with a full sample, Alaska Airlines, flew 433 at 83.4% on time.
Set against the rest of the country, United's SAN to DEN record is 8 points better than the US average of 77.6%. That gap is worth roughly 78 fewer late arrivals for every thousand flights.
Key figures
On time
85.4%
Arrivals under 15 minutes late, of 2,058 completed flights
Avg delay
65 min
Across delayed arrivals only, not all flights
Cancelled
0.77%
National rate is 1.81%
Whole route
79.2%
Every carrier on SAN to DEN, 5,947 flights
These figures cover 2,081 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
United against every carrier on SAN to DEN
United flew 2,081 of the 5,947 flights on SAN to DEN, about 35% of it. Its 85.4% on time is 6 points better than the route as a whole, which runs 79.2%. Ranked by on-time rate it is first 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. Alaska Airlines arrives on time 83.4% 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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines (this page) | 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 | 2,387 | 72.4% | 57 min | 0.75% | C+ |
Alaska leads Southwest by 11 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
United flight numbers on SAN to DEN
Departure window
When United runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 19 points, against 11 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am350 flights92.0%
- 8am–11am365 flights90.1%
- 11am–2pm728 flights85.8%
- 2pm–5pm364 flights73.5%
- 5pm–8pm272 flights85.1%
- 8pm–5am2 flights—
Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 92.0% of the time, against 73.5% for the afternoon window. That is 19 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 728 flights scheduled in it.
Across the year
United on SAN to DEN through the year
July is the worst month at 74.2% on time, 19 points below April, the best at 92.8%. 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. July was the busiest month here, with 184 flights.
Across the week, Saturday is the strongest day at 90.4% on time and Thursday the weakest at 81.1%. 9 points is a smaller lever than departure hour, but it is free.
Delay causes
Why United runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 47% of the 19,000 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.
- 47%Late-arriving aircraft
- 36%National Airspace System
- 15%Carrier
- 2%Extreme weather
47% 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 19,000 reported delay minutes here, that single category outweighs weather by 25 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 19,437 reported delay minutes.
36% 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 6,960 minutes out of 19,000, against a national NAS share of 21%.
Cancellations are rare at 0.77%, 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
5.2% 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 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 is a different operation and performs like one: it runs 79.8% on time across 2,081 flights, 6 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 6 points of difference.
The sample behind these figures is 2,081 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 United on SAN to DEN
Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 92.8% on time and July 74.2%, a swing of 19 points. If the dates move at all, move them out of July before you think about anything else. 2,058 completed flights over 12 months sit behind that.
Related
Where to go next
- SAN to DEN, every carrier
- United on DEN to SAN, the return leg
- Alaska Airlines on SAN to DEN83.4%
- Frontier Airlines on SAN to DEN81.6%
- SkyWest Airlines on SAN to DEN79.2%
- Southwest Airlines on SAN to DEN72.4%
- United 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
- Same route, different airline: where the carrier you pick matters most
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.