Route reliability record
SAN→DEN
San Diego to Denver
- Flights
- 5,880
- Period
- June 2025 to May 2026
- Distance
- 853 mi
- Carriers
- 5
This route lands a B+, about a point better than the national rate of 77.4%. About one flight in five arrive 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 5,880 flights, of which United Airlines flew 2,090 at 83.9% on time.
United Airlines is the most reliable of the four carriers covered here at 83.9% on time across 2,090 flights.
Key figures
On time
78.7%
Arrivals under 15 minutes late, of 5,806 completed flights
Avg delay
63 min
Across delayed arrivals only, not all flights
Cancelled
0.92%
National rate is 1.80%
Best carrier
United
83.9% on time across 2,090 flights
These figures cover 5,880 flights between June 2025 and May 2026. The median arrival is 7 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
Which airline is most reliable on SAN to DEN
The choice of carrier is not cosmetic here. United Airlines arrives on time 83.9% of the time; Southwest Airlines manages 73.0%. 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 | 2,090 | 83.9% | 67 min | 0.77% | B+ |
| Alaska Airlines | 390 | 82.1% | 58 min | 1.28% | B |
| SkyWest Airlinesthin sample | 295 | 81.0% | 45 min | 1.69% | B |
| Frontier Airlines | 718 | 79.4% | 78 min | 1.11% | B |
| Southwest Airlines | 2,387 | 73.0% | 59 min | 0.84% | C+ |
United leads Southwest by 11 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 27 points, against 11 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,143 flights87.4%
- 8am–11am1,122 flights89.4%
- 11am–2pm1,391 flights78.6%
- 2pm–5pm1,084 flights62.6%
- 5pm–8pm673 flights73.0%
- 8pm–5am467 flights77.3%
Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 89.4% of the time, against 62.6% for the afternoon window. That is 27 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on.
Across the year
When delays peak on this route
This route's year swings by 23 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
June is the worst month at 63.6% on time, 23 points below January, the best at 86.6%. 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.
Across the week, Saturday is the strongest day at 86.8% on time and Friday the weakest at 72.7%. 14 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Late-arriving aircraft accounts for 44% of the 78,000 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.
- 44%Late-arriving aircraft
- 32%National Airspace System
- 22%Carrier
- 2%Extreme weather
- 0%Security
44% 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 78,000 reported delay minutes here, that single category outweighs weather by 23 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 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 89.4% on time here.
Cancellations sit at 0.92% against a national 1.80%, which is ordinary. Diversions add another 0.34%.
Connections and stage length
What a delay here actually costs
7.1% of arrivals land an hour or more late, close to the national 8.2%. 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 are the about an hour kind, 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 75.8% on time across 5,882 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 5,880 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 this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 86.6% on time and June 63.6%, a swing of 23 points. If the dates move at all, move them out of June before you think about anything else.
Common questions
SAN to DEN questions
How often is SAN to DEN delayed?
About one flight in five arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 21.3% of the 5,880 flights in this analysis, against 22.6% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SAN to DEN?
United Airlines leads at 83.9% on time across 2,090 flights. Southwest Airlines is at the other end on 73.0%, a gap of 11 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on SAN to DEN?
The 8am–11am departure window is the strongest at 89.4% on time. The 2pm–5pm window is the weakest at 62.6%, 27 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are June delays on SAN to DEN?
June is the weakest month at 63.6% on time, compared with 86.6% in January. Across the year that is 23 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- DEN to SAN — the return legseparate record
- San Diego International (SAN) delay statistics
- Denver International (DEN) delay statistics
- United Airlines on-time record83.9%
- Alaska Airlines on-time record82.1%
- SkyWest Airlines on-time record81.0%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. SAN to DEN and DEN to SAN are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, June 2025 to May 2026. Updated monthly. How this data is collected.