Carrier route record

WNSLC→DEN

Southwest Airlines · Salt Lake City to Denver

Flights: 2,328
Period: July 2025 to June 2026
Share of route: 30%
Carriers: 5

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

Southwest on SLC to DEN sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 5 points worse than the national rate of 77.6%. The late ones land about 50 minutes behind schedule. That rests on 2,328 flights. The strongest carrier on the route with a full sample, SkyWest Airlines, flew 1,395 at 84.6% on time.

SkyWest Airlines is the most reliable of the four carriers covered here at 84.6% on time across 1,395 flights.

On time

72.4%

Arrivals under 15 minutes late, of 2,306 completed flights

Avg delay

51 min

Across delayed arrivals only, not all flights

Cancelled

0.69%

National rate is 1.81%

Whole route

77.8%

Every carrier on SLC to DEN, 7,757 flights

These figures cover 2,328 flights between July 2025 and June 2026. The median arrival is 2 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 SLC to DEN

Southwest flew 2,328 of the 7,757 flights on SLC to DEN, about 30% of it. Its 72.4% on time is 5 points worse than the route as a whole, which runs 77.8%. Ranked by on-time rate it is last of five carriers on the route, where the range runs from SkyWest at 84.6% to Southwest at 72.4%.

The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 84.6% of the time; United Airlines manages 78.0%. Sample sizes sit next to every figure, because a two-point gap across 1,332 flights means less than a ten-point one.

On-time performance by carrier on SLC to DEN
Airline	Flights	On time	Avg delay	Cancelled	Grade
SkyWest Airlines	1,395	84.6%	76 min	0.65%	B+
Delta Air Lines	1,690	79.4%	64 min	0.24%	B+
Frontier Airlines	1,012	78.1%	73 min	0.89%	B+
United Airlines	1,332	78.0%	61 min	0.38%	B+
Southwest Airlines (this page)	2,328	72.4%	51 min	0.69%	C+

SkyWest leads United by 7 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 36 points, against 7 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am480 flights94.1%
8am–11am479 flights71.8%
11am–2pm391 flights77.7%
2pm–5pm522 flights57.7%
5pm–8pm311 flights64.1%
8pm–5am145 flights59.3%

Scale runs 50% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 94.1% of the time, against 57.7% for the afternoon window. That is 36 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 522 flights scheduled in it.

Across the year

Southwest on SLC to DEN through the year

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

July is the worst month at 63.4% on time, 19 points below November, the best at 82.4%. 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. July was the busiest month here, with 222 flights.

Across the week, Saturday is the strongest day at 80.7% on time and Friday the weakest at 66.5%. 14 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. National Airspace System accounts for 47% of the 32,000 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.

National Airspace System
47%
Late-arriving aircraft
36%
Carrier
15%
Extreme weather
1%
Security
0%

36% 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 32,000 reported delay minutes here, that single category outweighs weather by 33 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 32,161 reported delay minutes.

47% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 15,000 minutes out of 32,000, against a national NAS share of 21%.

Cancellations are rare at 0.69%, 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

6.8% 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 last about 50 minutes, which a normal layover absorbs.

At 391 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 5am–8am window matters as much as it does.

The return leg runs 71.2% on time across 2,329 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 2,328 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 Southwest on SLC to DEN

Put together: the calendar is the biggest lever here, not the carrier or the hour. November runs 82.4% on time and July 63.4%, a swing of 19 points. If the dates move at all, move them out of July before you think about anything else. 2,306 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