Route reliability record
SAN→DEN
San Diego to Denver
- Flights
- 6,134
- Period
- September 2025 to August 2026
- Distance
- 853 mi
- Carriers
- 5
This route lands a B, about a point better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 6,134 SAN to DEN flights, of which United Airlines flew 2,067 at 85.7% on time.
Best time to fly SAN to DEN: a 5am–8am departure, ideally on a Saturday. Flights in that window arrived on time 89.9% of the time and Saturday flights 86.6%, against 78.4% for the route overall.
United Airlines is the most reliable of the five carriers covered here at 85.7% on time across 2,067 flights.
Key figures
On time
78.4%
Arrivals under 15 minutes late, of 6,053 completed flights
Avg delay
63 min
Across delayed arrivals only, not all flights
Cancelled
1.03%
National rate is 1.89%
Best carrier
United
85.7% on time across 2,067 flights
These figures cover 6,134 flights between September 2025 and August 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.
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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 85.7% of the time; Southwest Airlines manages 71.0%. Sample sizes sit next to every figure, because a two-point gap across 2,404 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 2,067 | 85.7% | 72 min | 0.63% | A+ |
| Alaska Airlines | 557 | 84.1% | 57 min | 0.90% | B+ |
| Frontier Airlines | 702 | 81.4% | 87 min | 1.99% | B |
| SkyWest Airlines | 404 | 72.1% | 52 min | 3.47% | C− |
| Southwest Airlines | 2,404 | 71.0% | 58 min | 0.71% | C+ |
SkyWest Airlines cancels 3.5% of what it schedules here, the highest in the table. A cancelled flight never appears in an on-time rate, so read that column alongside the punctuality one rather than after it.
Flight by flight
Flights on SAN to DEN
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly San Diego to Denver
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SAN → DENSan Diego to Denver | United Airlines | 85.2% | 85.7% | 0.63% | 5am–8am, Sat | UA 1337 11:00 |
| 2. SAN → DENSan Diego to Denver | Alaska Airlines | 83.3% | 84.1% | 0.90% | 5am–8am, Sat | — |
| 3. SAN → DENSan Diego to Denver | Frontier Airlines | 79.8% | 81.4% | 1.99% | 5am–8am, Sun | F9 2818 06:25 |
| 4. SAN → DENSan Diego to Denver | Southwest Airlines | 70.5% | 71.0% | 0.71% | 5am–8am, Sat | — |
| 5. SAN → DENSan Diego to Denver | SkyWest Airlines | 69.6% | 72.1% | 3.47% | 8am–11am, Sat | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 30 points, against 15 points between the best and worst carrier.
- 5am–8am1,209 flights89.9%
- 8am–11am1,202 flights87.5%
- 11am–2pm1,316 flights79.2%
- 2pm–5pm1,209 flights59.7%
- 5pm–8pm671 flights73.2%
- 8pm–5am527 flights78.6%
Scale runs 50% to 95%.
Book the early departure. Flights leaving between 5am–8am arrive on time 89.9% of the time, against 59.7% for the afternoon window. That is 30 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 1,316 flights scheduled in it.
Explore
Filter SAN to DEN by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On SAN to DEN, the best departure window is 5am–8am at 89.9% on time and the worst is 2pm–5pm at 59.7%, a wide gap of 30.2 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am89.9%
- 8–11am87.5%
- 11am–2pm79.2%
- 2–5pm59.7%
- 5–8pm73.2%
- 8pm–5am78.6%
best all US flightsScale 50% to 95%.
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.
August is the worst month at 63.9% 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. July was the busiest month here, with 544 flights.
Across the week, Saturday is the strongest day at 86.6% on time and Thursday the weakest at 71.4%, a spread of 15 points.
Delay causes
Why this route gets delayed
Late-arriving aircraft accounts for 49% of the 83,000 delay minutes carriers reported here, and the remaining four split what is left.
- 49%Late-arriving aircraft
- 29%National Airspace System
- 19%Carrier
- 3%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. Across 83,000 reported delay minutes here, that single category outweighs weather by 19 to one. The split is drawn from 82,561 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 89.9% on time here.
Cancellations sit at 1.03% against a national 1.89%, which is ordinary. Diversions add another 0.29%.
Connections and stage length
What a delay here actually costs
7.4% of arrivals land an hour or more late, close to the national 8.3%, so 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.
The return leg is a different operation and performs like one: it runs 73.8% on time across 6,152 flights, 5 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 5 points of difference.
The sample behind these figures is 6,134 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.
Work out the risk of missing a connection in DEN after this flight
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 August 63.9%, a swing of 23 points. If the dates move at all, move them out of August before you think about anything else. 6,053 completed flights over 12 months sit behind that.
Common questions
SAN to DEN questions
How often is SAN to DEN delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 21.6% of the 6,134 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SAN to DEN?
United Airlines leads at 85.7% on time across 2,067 flights. Southwest Airlines is at the other end on 71.0%, a gap of 15 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 5am–8am departure window is the strongest at 89.9% on time. The 2pm–5pm window is the weakest at 59.7%, 30 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 August delays on SAN to DEN?
August is the weakest month at 63.9% 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 SAN to DEN85.7%
- Alaska Airlines on SAN to DEN84.1%
- Frontier Airlines on SAN to DEN81.4%
- SkyWest Airlines on SAN to DEN72.1%
- Southwest Airlines on SAN to DEN71.0%
- SAN to SFO, a related route59.5%
- PHX to DEN, a related route76.7%
- SAN to PHX, a related route73.5%
- United Airlines on-time record85.7%
- Alaska Airlines on-time record84.1%
- Frontier Airlines on-time record81.4%
- Why the first flight of the morning is statistically safest
- Same route, different airline: where the carrier you pick matters most
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.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.