Route reliability record
DEN→SAN
Denver to San Diego
- Flights
- 6,152
- Period
- September 2025 to August 2026
- Distance
- 853 mi
- Carriers
- 5
This route sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, 4 points worse than the national rate of 77.3%. The late ones land about an hour behind schedule. That rests on 6,152 DEN to SAN flights, of which Alaska Airlines flew 557 at 82.2% on time.
Best time to fly DEN to SAN: a 5am–8am departure, ideally on a Saturday. Flights in that window arrived on time 91.5% of the time and Saturday flights 81.1%, against 73.8% for the route overall.
Alaska Airlines is the most reliable of the five carriers covered here at 82.2% on time across 557 flights.
Key figures
On time
73.8%
Arrivals under 15 minutes late, of 6,086 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
0.83%
National rate is 1.89%
Best carrier
Alaska
82.2% on time across 557 flights
These figures cover 6,152 flights between September 2025 and August 2026. Beyond the headline rate, 8.0% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Which airline is most reliable on DEN to SAN
The choice of carrier is not cosmetic here. Alaska Airlines arrives on time 82.2% of the time; Southwest Airlines manages 67.3%. Sample sizes sit next to every figure, because a two-point gap across 2,422 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Alaska Airlines | 557 | 82.2% | 52 min | 1.08% | B |
| Frontier Airlines | 701 | 80.1% | 66 min | 1.43% | B |
| United Airlines | 2,067 | 77.9% | 59 min | 0.34% | B+ |
| SkyWest Airlines | 405 | 68.6% | 47 min | 3.21% | C− |
| Southwest Airlines | 2,422 | 67.3% | 55 min | 0.62% | C+ |
SkyWest Airlines cancels 3.2% 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 DEN to SAN
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 Denver to San Diego
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. DEN → SANDenver to San Diego | Alaska Airlines | 81.3% | 82.2% | 1.08% | 5am–8am, Wed | — |
| 2. DEN → SANDenver to San Diego | Frontier Airlines | 79.0% | 80.1% | 1.43% | 5am–8am, Tue | F9 4989 22:29 |
| 3. DEN → SANDenver to San Diego | United Airlines | 77.6% | 77.9% | 0.34% | 5am–8am, Sat | UA 2309 07:45 |
| 4. DEN → SANDenver to San Diego | Southwest Airlines | 66.9% | 67.3% | 0.62% | 5am–8am, Tue | — |
| 5. DEN → SANDenver to San Diego | SkyWest Airlines | 66.4% | 68.6% | 3.21% | 5am–8am, Tue | — |
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 32 points, against 15 points between the best and worst carrier.
- 5am–8am1,063 flights91.5%
- 8am–11am721 flights81.6%
- 11am–2pm1,351 flights76.7%
- 2pm–5pm821 flights72.1%
- 5pm–8pm987 flights59.7%
- 8pm–5am1,209 flights62.6%
Scale runs 50% to 95%.
The 5pm–8pm window is where this operation falls apart: 59.7% on time, against 91.5% 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 11am–2pm window is the busiest, with 1,351 flights scheduled in it.
Explore
Filter DEN to SAN 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 DEN to SAN, the best departure window is 5am–8am at 91.5% on time and the worst is 5pm–8pm at 59.7%, a wide gap of 31.8 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am91.5%
- 8–11am81.6%
- 11am–2pm76.7%
- 2–5pm72.1%
- 5–8pm59.7%
- 8pm–5am62.6%
best all US flightsScale 50% to 95%.
Across the year
When delays peak on this route
This route's year swings by 32 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 52.4% on time, 32 points below February, the best at 84.1%. 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. August was the busiest month here, with 553 flights.
Across the week, Saturday is the strongest day at 81.1% on time and Thursday the weakest at 67.7%, a spread of 13 points.
Delay causes
Why this route gets delayed
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 90,000 reported delay minutes.
- 40%Late-arriving aircraft
- 30%National Airspace System
- 28%Carrier
- 1%Extreme weather
- 0%Security
40% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 90,000 reported delay minutes here, that single category outweighs weather by 36 to one. The split is drawn from 89,574 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 91.5% on time here.
Cancellations are rare at 0.83%, below the national 1.89% 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 actually costs
8.0% 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 78.4% on time across 6,134 flights, 5 points above 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 6,152 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 SAN 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. February runs 84.1% on time and August 52.4%, a swing of 32 points. If the dates move at all, move them out of August before you think about anything else. 6,086 completed flights over 12 months sit behind that.
Common questions
DEN to SAN questions
How often is DEN to SAN delayed?
About one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 26.2% of the 6,152 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on DEN to SAN?
Alaska Airlines leads at 82.2% on time across 557 flights. Southwest Airlines is at the other end on 67.3%, 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 DEN to SAN?
The 5am–8am departure window is the strongest at 91.5% on time. The 5pm–8pm window is the weakest at 59.7%, 32 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 DEN to SAN?
August is the weakest month at 52.4% on time, compared with 84.1% in February. Across the year that is 32 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
- SAN to DEN — the return legseparate record
- Denver International (DEN) delay statistics
- San Diego International (SAN) delay statistics
- Alaska Airlines on DEN to SAN82.2%
- Frontier Airlines on DEN to SAN80.1%
- United Airlines on DEN to SAN77.9%
- SkyWest Airlines on DEN to SAN68.6%
- Southwest Airlines on DEN to SAN67.3%
- DEN to PHX, a related route75.6%
- SFO to SAN, a related route62.2%
- DEN to SLC, a related route78.2%
- Alaska Airlines on-time record82.2%
- Frontier Airlines on-time record80.1%
- United Airlines on-time record77.9%
- Why the first flight of the morning is statistically safest
- Same route, different airline: where the carrier you pick matters most
Direction matters. DEN to SAN and SAN to DEN 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.