Route reliability record

DEN→SLC

Denver to Salt Lake City

Flights: 7,765
Period: June 2025 to May 2026
Distance: 391 mi
Carriers: 5

This route lands a B+, level with the national rate of 77.4%. Roughly 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 7,765 flights, of which Delta Air Lines flew 1,689 at 81.8% on time.

Delta Air Lines is the most reliable of the five carriers covered here at 81.8% on time across 1,689 flights.

On time

77.2%

Arrivals under 15 minutes late, of 7,718 completed flights

Avg delay

63 min

Across delayed arrivals only, not all flights

Cancelled

0.48%

National rate is 1.80%

Best carrier

Delta

81.8% on time across 1,689 flights

These figures cover 7,765 flights between June 2025 and May 2026. The median arrival is 5 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 SLC

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 81.8% of the time; Southwest Airlines manages 71.3%. Sample sizes sit next to every figure, because a two-point gap across 2,347 flights means less than a ten-point one.

On-time performance by carrier on DEN to SLC
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	1,689	81.8%	85 min	0.36%	B+
Frontier Airlines	995	80.6%	63 min	0.50%	B+
SkyWest Airlines	1,381	79.3%	64 min	0.87%	B+
United Airlines	1,353	77.3%	60 min	0.22%	B+
Southwest Airlines	2,347	71.3%	53 min	0.47%	C+

Delta 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 23 points, against 11 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am903 flights89.1%
8am–11am1,256 flights87.7%
11am–2pm1,550 flights80.7%
2pm–5pm1,365 flights77.8%
5pm–8pm1,445 flights65.8%
8pm–5am1,246 flights66.4%

Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 89.1% of the time, against 65.8% for the evening window. That is 23 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on.

Across the year

When delays peak on this route

This route's year swings by 25 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.February best, July worst

July is the worst month at 59.3% on time, 25 points below February, the best at 84.1%. 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.

Across the week, Saturday is the strongest day at 82.1% on time and Sunday the weakest at 73.9%. 8 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 46% of the 110,000 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
46%
Carrier
37%
National Airspace System
14%
Extreme weather
3%
Security
0%

46% 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 110,000 reported delay minutes here, that single category outweighs weather by 14 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 largest share of delay minutes, 37%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 41,000 of the 110,000 delay minutes reported here.

Cancellations are rare at 0.48%, below the national 1.80% 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

7.4% of arrivals land an hour or more late, close to the national 8.2%. 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 76.7% on time across 7,763 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 7,765 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. February runs 84.1% on time and July 59.3%, a swing of 25 points. If the dates move at all, move them out of July before you think about anything else.

Common questions

DEN to SLC questions

How often is DEN to SLC delayed?

Roughly 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 22.8% of the 7,765 flights in this analysis, against 22.6% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on DEN to SLC?

Delta Air Lines leads at 81.8% on time across 1,689 flights. Southwest Airlines is at the other end on 71.3%, 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 SLC?

The 5am–8am departure window is the strongest at 89.1% on time. The 5pm–8pm window is the weakest at 65.8%, 23 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 SLC?

July is the weakest month at 59.3% on time, compared with 84.1% in February. Across the year that is 25 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 SLC and SLC 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, June 2025 to May 2026. Updated monthly. How this data is collected.

Key figures