Route reliability record

SAN→DEN

San Diego to Denver

Flights: 5,947
Period: July 2025 to June 2026
Distance: 853 mi
Carriers: 5

This route lands a B+, 2 points better than the national rate of 77.6%. 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 5,947 flights, of which United Airlines flew 2,081 at 85.4% on time.

United Airlines is the most reliable of the four carriers covered here at 85.4% on time across 2,081 flights.

On time

79.2%

Arrivals under 15 minutes late, of 5,875 completed flights

Avg delay

60 min

Across delayed arrivals only, not all flights

Cancelled

0.89%

National rate is 1.81%

Best carrier

United

85.4% on time across 2,081 flights

These figures cover 5,947 flights between July 2025 and June 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 85.4% 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.

On-time performance by carrier on SAN to DEN
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	2,387	72.4%	57 min	0.75%	C+

The spread between United and Southwest is 13 points, wide enough that it should decide the booking. On a hundred trips that is 13 more arrivals inside the on-time window.

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 13 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,159 flights88.5%
8am–11am1,153 flights89.0%
11am–2pm1,362 flights79.5%
2pm–5pm1,119 flights62.3%
5pm–8pm673 flights73.6%
8pm–5am481 flights79.7%

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 89.0% of the time, against 62.3% 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. The 11am–2pm window is the busiest, with 1,362 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 18 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.

Darker means more delays. Figures are on-time percentages.January best, July worst

July is the worst month at 68.5% on time, 18 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. March was the busiest month here, with 538 flights.

Across the week, Saturday is the strongest day at 86.8% on time and Friday the weakest at 73.0%. 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 48% of the 74,000 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.

Late-arriving aircraft
48%
National Airspace System
30%
Carrier
21%
Extreme weather
2%
Security
0%

48% 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 74,000 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 73,709 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 89.0% on time here.

Cancellations are rare at 0.89%, 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 actually costs

6.7% 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 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 is a different operation and performs like one: it runs 75.6% on time across 5,949 flights, 4 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 4 points of difference.

The sample behind these figures is 5,947 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 July 68.5%, a swing of 18 points. If the dates move at all, move them out of July before you think about anything else. 5,875 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 arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 20.8% of the 5,947 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on SAN to DEN?

United Airlines leads at 85.4% on time across 2,081 flights. Southwest Airlines is at the other end on 72.4%, a gap of 13 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 89.0% on time. The 2pm–5pm window is the weakest at 62.3%, 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 July delays on SAN to DEN?

July is the weakest month at 68.5% on time, compared with 86.6% in January. Across the year that is 18 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

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, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures