Route reliability record

SAN→SLC

San Diego to Salt Lake City

Flights: 2,961
Period: July 2025 to June 2026
Distance: 626 mi
Carriers: 4

This route earns a B+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.6%. When something does go wrong the average delay runs about an hour. That rests on 2,961 flights, of which Delta Air Lines flew 1,732 at 88.7% on time.

Delta Air Lines is the most reliable of the three carriers covered here at 88.7% on time across 1,732 flights.

On time

84.4%

Arrivals under 15 minutes late, of 2,934 completed flights

Avg delay

65 min

Across delayed arrivals only, not all flights

Cancelled

0.71%

National rate is 1.81%

Best carrier

Delta

88.7% on time across 1,732 flights

These figures cover 2,961 flights between July 2025 and June 2026. The median arrival is 9 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 SLC

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 88.7% of the time; Southwest Airlines manages 76.6%. Sample sizes sit next to every figure, because a two-point gap across 408 flights means less than a ten-point one.

On-time performance by carrier on SAN to SLC
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	1,732	88.7%	77 min	0.81%	A+
Frontier Airlinesthin sample	133	83.3%	87 min	0.75%	B+
SkyWest Airlines	688	78.4%	61 min	0.73%	B+
Southwest Airlines	408	76.6%	45 min	0.25%	B+

The spread between Delta and Southwest is 12 points, wide enough that it should decide the booking. On a hundred trips that is 12 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 26 points, against 12 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am396 flights95.7%
8am–11am671 flights90.2%
11am–2pm579 flights83.9%
2pm–5pm211 flights70.2%
5pm–8pm979 flights80.3%
8pm–5am125 flights75.8%

Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 95.7% of the time, against 70.2% for the afternoon window. That is 26 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 979 flights scheduled in it.

Across the year

When delays peak on this route

Twelve months, one bar each, drawn from the same 2,961 flights. The strip shows how much of this route's record is set by the calendar rather than by the operation.

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

July is the worst month at 79.1% on time, 9 points below April, the best at 88.5%. 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 294 flights.

Across the week, Monday is the strongest day at 89.1% on time and Thursday the weakest at 78.7%. 10 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 56% of the 30,000 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
56%
Carrier
31%
National Airspace System
10%
Extreme weather
3%
Security
0%

56% 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 30,000 reported delay minutes here, that single category outweighs weather by 19 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 29,971 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 95.7% on time here.

Cancellations are rare at 0.71%, 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

5.2% 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 626 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 83.2% on time across 2,958 flights, within about a point 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 2,961 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: take the 5am–8am departure, avoid July if the dates are flexible, and if two carriers are within a few dollars of each other, Delta is the one with the record behind it. None of that guarantees an on-time arrival; it moves the odds by 26 points, which is the most any booking decision can do. 2,934 completed flights over 12 months sit behind that.

Common questions

SAN to SLC questions

How often is SAN to SLC delayed?

About one flight in six arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 15.6% of the 2,961 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 SLC?

Delta Air Lines leads at 88.7% on time across 1,732 flights. Southwest Airlines is at the other end on 76.6%, a gap of 12 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 SLC?

The 5am–8am departure window is the strongest at 95.7% on time. The 2pm–5pm window is the weakest at 70.2%, 26 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 SLC?

July is the weakest month at 79.1% on time, compared with 88.5% in April. Across the year that is 9 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 SLC and SLC 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