Carrier route record

WNSAN→SLC

Southwest Airlines · San Diego to Salt Lake City

Flights: 408
Period: July 2025 to June 2026
Share of route: 14%
Carriers: 4

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.

Southwest on SAN to SLC lands a B+, about a point worse than the national rate of 77.6%. About one flight in four arrives 15 minutes late or worse, and those flights are late by about 45 minutes on average. That is a workable record, not a spotless one. That rests on 408 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 1,732 at 88.7% on time.

The US average over the same twelve months is 77.6%, so there is little to separate Southwest on SAN to SLC from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

76.6%

Arrivals under 15 minutes late, of 406 completed flights

Avg delay

45 min

Across delayed arrivals only, not all flights

Cancelled

0.25%

National rate is 1.81%

Whole route

84.4%

Every carrier on SAN to SLC, 2,961 flights

These figures cover 408 flights between July 2025 and June 2026. The median arrival is 3 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

Southwest against every carrier on SAN to SLC

Southwest flew 408 of the 2,961 flights on SAN to SLC, about 14% of it. Its 76.6% on time is 8 points worse than the route as a whole, which runs 84.4%. Ranked by on-time rate it is last of four carriers on the route, where the range runs from Delta at 88.7% to Southwest at 76.6%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 88.7% of the time; SkyWest Airlines manages 78.4%. Sample sizes sit next to every figure, because a two-point gap across 688 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 (this page)	408	76.6%	45 min	0.25%	B+

Delta leads SkyWest by 10 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Departure window

When Southwest runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 28 points, against 10 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am19 flights—
8am–11am78 flights93.4%
11am–2pm138 flights76.8%
2pm–5pm110 flights68.2%
5pm–8pm40 flights65.0%
8pm–5am23 flights—

Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.

Book the morning departure. Flights leaving between 8am–11am arrive on time 93.4% of the time, against 65.0% for the evening window. That is 28 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 138 flights scheduled in it.

Across the year

Southwest on SAN to SLC through the year

Darker means more delays. Figures are on-time percentages.September best, May worst

September is the best month on the calendar at 93.3% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. December was the busiest month here, with 42 flights.

Across the week, Saturday is the strongest day at 86.2% on time and Friday the weakest at 63.8%. 22 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Southwest runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 72% of the 4,234 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
72%
Carrier
21%
National Airspace System
7%
Security
1%

72% 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 4,234 reported delay minutes here, that single category outweighs weather by 72 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 4,234 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 93.4% on time here.

Cancellations are rare at 0.25%, 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 costs

Badly late arrivals are rare here: only 4.9% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

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 75.8% on time across 408 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.

One caution: this is a thin sample. 408 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.

What to do with this

Booking Southwest on SAN to SLC

Put together: treat all of this as provisional. 408 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 76.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 406 completed flights over 12 months sit behind that.

Where to go next

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures