Route reliability record

DEN→SAT

Denver to San Antonio

Flights: 3,030
Period: July 2025 to June 2026
Distance: 794 mi
Carriers: 4

This route lands a B+, about a point worse than the national rate of 77.6%. About one flight in four 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 3,030 flights, of which United Airlines flew 1,205 at 81.9% on time.

United Airlines is the most reliable of the three carriers covered here at 81.9% on time across 1,205 flights.

On time

76.5%

Arrivals under 15 minutes late, of 3,018 completed flights

Avg delay

57 min

Across delayed arrivals only, not all flights

Cancelled

0.23%

National rate is 1.81%

Best carrier

United

81.9% on time across 1,205 flights

These figures cover 3,030 flights between July 2025 and June 2026. The median arrival is 4 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 DEN to SAT

The choice of carrier is not cosmetic here. United Airlines arrives on time 81.9% of the time; Southwest Airlines manages 70.7%. Sample sizes sit next to every figure, because a two-point gap across 1,434 flights means less than a ten-point one.

On-time performance by carrier on DEN to SAT
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,205	81.9%	63 min	0.25%	B+
Frontier Airlines	372	81.4%	60 min	0.27%	B+
SkyWest Airlinesthin sample	19	78.9%	192 min	0.00%	B+
Southwest Airlines	1,434	70.7%	52 min	0.21%	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 30 points, against 11 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am113 flights85.6%
8am–11am682 flights89.3%
11am–2pm752 flights83.9%
2pm–5pm499 flights71.0%
5pm–8pm667 flights65.8%
8pm–5am317 flights59.4%

Scale runs 50% to 95%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 59.4% on time, against 89.3% for the 8am–11am 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 752 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 30 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.November best, July worst

July is the worst month at 57.6% on time, 30 points below November, the best at 87.6%. 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 299 flights.

Across the week, Wednesday is the strongest day at 83.4% on time and Friday the weakest at 72.5%. 11 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 58% of the 40,000 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
58%
Carrier
28%
National Airspace System
12%
Extreme weather
2%
Security
0%

58% 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 40,000 reported delay minutes here, that single category outweighs weather by 30 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 40,303 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 89.3% on time here.

Cancellations are rare at 0.23%, 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

7.2% 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 are the about an hour kind, which a normal layover absorbs.

The 794 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 81.0% on time across 3,027 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 3,030 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. November runs 87.6% on time and July 57.6%, a swing of 30 points. If the dates move at all, move them out of July before you think about anything else. 3,018 completed flights over 12 months sit behind that.

Common questions

DEN to SAT questions

How often is DEN to SAT delayed?

About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 23.5% of the 3,030 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on DEN to SAT?

United Airlines leads at 81.9% on time across 1,205 flights. Southwest Airlines is at the other end on 70.7%, 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 DEN to SAT?

The 8am–11am departure window is the strongest at 89.3% on time. The 8pm–5am window is the weakest at 59.4%, 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 July delays on DEN to SAT?

July is the weakest month at 57.6% on time, compared with 87.6% in November. Across the year that is 30 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. DEN to SAT and SAT to DEN 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