Route reliability record

SLC→DEN

Salt Lake City to Denver

Flights: 7,757
Period: July 2025 to June 2026
Distance: 391 mi
Carriers: 5

This route lands a B+, level with the national rate of 77.6%. Roughly 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 7,757 flights, of which SkyWest Airlines flew 1,395 at 84.6% on time.

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

On time

77.8%

Arrivals under 15 minutes late, of 7,694 completed flights

Avg delay

61 min

Across delayed arrivals only, not all flights

Cancelled

0.55%

National rate is 1.81%

Best carrier

SkyWest

84.6% on time across 1,395 flights

These figures cover 7,757 flights between July 2025 and June 2026. The median arrival is 6 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 SLC to DEN

The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 84.6% of the time; Southwest Airlines manages 72.4%. Sample sizes sit next to every figure, because a two-point gap across 2,328 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	2,328	72.4%	51 min	0.69%	C+

The spread between SkyWest 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 24 points, against 12 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,475 flights90.3%
8am–11am1,807 flights77.4%
11am–2pm1,345 flights84.3%
2pm–5pm1,273 flights66.3%
5pm–8pm1,175 flights69.9%
8pm–5am682 flights74.1%

Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 90.3% of the time, against 66.3% for the afternoon window. That is 24 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 1,807 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 21 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 63.5% on time, 21 points below November, the best at 84.2%. 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 688 flights.

Across the week, Saturday is the strongest day at 83.2% on time and Friday the weakest at 73.3%. 10 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 104,000 reported delay minutes.

National Airspace System
34%
Carrier
33%
Late-arriving aircraft
31%
Extreme weather
2%
Security
0%

34% 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 36,000 minutes out of 104,000, against a national NAS share of 21%. The split is drawn from 104,254 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 90.3% on time here.

Cancellations are rare at 0.55%, 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.

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 77.5% on time across 7,758 flights, within half 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 7,757 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 84.2% on time and July 63.5%, a swing of 21 points. If the dates move at all, move them out of July before you think about anything else. 7,694 completed flights over 12 months sit behind that.

Common questions

SLC to DEN questions

How often is SLC to DEN delayed?

Roughly 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 22.2% of the 7,757 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on SLC to DEN?

SkyWest Airlines leads at 84.6% on time across 1,395 flights. Southwest Airlines is at the other end on 72.4%, 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 SLC to DEN?

The 5am–8am departure window is the strongest at 90.3% on time. The 2pm–5pm window is the weakest at 66.3%, 24 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 SLC to DEN?

July is the weakest month at 63.5% on time, compared with 84.2% in November. Across the year that is 21 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. SLC to DEN and DEN to SLC 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