Guide
Denver, Salt Lake City, Phoenix and Las Vegas: the Mountain West hubs
Salt Lake City (SLC) leads the 60 busiest US airports at 84.2% on time, while Denver manages 76.6%. How the West's big hubs differ by month, hour and airline.
Salt Lake City and Denver sit less than 400 miles apart, share the same winter storms and sell the same connections to the same ski towns. Over September 2025 to August 2026, flights leaving Salt Lake City arrived on time 84.2% of the time. Flights leaving Denver managed 76.6%. That ranks Salt Lake City number 1 of the 60 airports with a page on this site, and Denver number 41.
An airport's number here covers the flights departing it: on time means arriving less than 15 minutes after schedule, among flights that operated. Denver's figure describes the leg a connecting passenger controls least. (By departures in this data, Denver is busier than Atlanta.)
US average 77.3%
70.0%90.0%
Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
Phoenix sits at 77.9% and Las Vegas at 76.9%, both close to the national 77.3%. Albuquerque, a much smaller field with 24,547 departures a year against Denver's 319,681, runs 83.1%. Size is part of the story, but not the whole of it: Salt Lake City, with 117,966 departures and a Delta hub bank structure, keeps pace with the small field.
Salt Lake City's flat day
The most distinctive thing about Salt Lake City is not its average. It is how little the average moves.
Nationally, departures in the 5am–8am window arrive on time 89.3% of the time and those in the 5pm–8pm window 68.0%, a gap of 21.3 points. At Salt Lake City the same gap is 12.0 points. At Denver it is 24.4.
Denver (DEN)76.6% overall
Salt Lake City (SLC)84.2% overall
Phoenix (PHX)77.9% overall
Las Vegas (LAS)76.9% overall
All panels share one scale, 60% to 95% on time. Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
The usual reason evening flights run late is rotation. An aircraft flies four to six legs a day, and every late arrival passes its delay to the next departure. The DOT's cause codes capture this as "late-arriving aircraft", which accounts for 40% of delay minutes nationally and 44% at Denver. At Salt Lake City it is 26%. The largest share there is charged to the airlines themselves, at 46%.
I read that split with caution. Delta's hubs put more delay under "air carrier" and less under "late-arriving aircraft" than the national split, and Endeavor Air never appears as a separate carrier at them in this data; I take that as a reporting convention, not proof of a better schedule. The flat day is the stronger evidence. Delta and its regional partner SkyWest fly most of Salt Lake City's departures, so the airport's figure is largely a reading of how one airline family runs one hub. Its worst month, August at 78.3%, compares with 77.3% for the whole country across the whole year.
Denver's problem is summer, not snow
Most travellers picture Denver's risk as a January blizzard. The monthly record points elsewhere. Denver's best month was November at 84.7% and its worst June at 67.1%. July ran 69.6%. January ran 82.3% and February 82.4%.
Denver (DEN)76.6% overall
Salt Lake City (SLC)84.2% overall
Phoenix (PHX)77.9% overall
Las Vegas (LAS)76.9% overall
All panels share one scale, 60% to 95% on time. Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
The summer dip fits what happens over the Front Range between June and August: thunderstorms build over the mountains in early afternoon and drift east across the airport, and a lightning cell within a few miles stops ramp work and can trigger ground stops. Those storms land squarely on Denver's weakest departure window. Departures between 5am and 8am ran 90.9% on time; those between 5pm and 8pm ran 66.5%.
Winter still matters, just differently. December was Denver's weakest month outside summer at 74.3%, when holiday volume meets the first serious storms and every departure queues for de-icing. And snow tends to show up as cancellations rather than delays: an on-time rate counts only flights that operated. Even so, Denver's annual cancellation rate of 0.78% sits below the national 1.89%. The airport has six runways and a snow operation built for the job, and it rarely closes for long.
Phoenix and Las Vegas in July
In the desert the calendar flips. Phoenix's best month was February at 83.4% and its worst July at 70.0%. Las Vegas ran best in January (83.1%) and worst in July (69.6%).
July is the worst month nationally too, at 71.7%, so part of the desert summer is simply the country's summer arriving on inbound aircraft. The local contributions are real, though. Extreme heat thins the air, which cuts the weight an aircraft can lift and can force payload restrictions on the hottest afternoons. The monsoon season brings afternoon thunderstorms and, at Phoenix, dust storms that can halt operations for an hour or more. Both hit hardest after midday. At Phoenix the 5am to 8am window ran 91.8% on time and the 5pm to 8pm window 69.4%. At Las Vegas the same pair was 90.8% and 66.9%.
Late-arriving aircraft make up 45% of delay minutes at Phoenix and 44% at Las Vegas, above the national share. Both are big point-to-point stations where most aircraft arrive from somewhere else, so a storm in Dallas at 2pm becomes a late departure in Phoenix at 6pm.
Southwest's weight at three of the four
Southwest is the largest carrier at Las Vegas and Phoenix and the second largest at Denver, behind United. Across its whole network Southwest ran 75.7% on time, and the gap between its early-morning and early-evening departures was 30.7 points against 20.1 for the median airline. A point-to-point schedule with quick turns has few spare aircraft to absorb a bad afternoon.
DEN average 76.6%
55.0%90.0%
Carriers with at least 1,000 scheduled flights at the airport. Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
At Denver the difference is stark. United and SkyWest, which together fly more than half of Denver's departures, ran above the airport's average, while Southwest ran well below it. The airline-at-airport pages for Southwest at Denver, Las Vegas and Phoenix show how steep its evening decline is at each field.
This is not a verdict on Southwest's cancellation rate, which at 0.92% sits well below the national 1.89%.
It is a reason to book its morning flights.
Where the delay minutes come from
Share of all delay minutes. Darker is a bigger share. Air traffic is the National Airspace System category; weather is extreme weather only.
Source: US DOT Bureau of Transportation Statistics, September 2025 to August 2026.
The cause split separates the two models. Denver, Phoenix, Las Vegas and Albuquerque all carry late-aircraft shares in the forties, the signature of delays passed down the day. Salt Lake City carries the lowest late-aircraft share of the five and the highest airline share. The National Aviation System category, which covers traffic volume, air traffic control programmes and most ordinary weather, is similar across all five, between about a sixth and a fifth of the minutes. Extreme weather, the DOT's narrow category, stays small everywhere, as it does nationally at 6%.
My call on the four hubs
Connecting across the West, prefer Salt Lake City where the fare and schedule allow. Its departures run 84.2% on time with a far flatter day, so a mid-afternoon connection there carries much less risk than the same connection at Denver.
If it has to be Denver, connect in the morning. The first two departure windows hold up well. From June to August, I would not book a connection that leaves Denver after 2pm; if there is no other option, give it at least 90 minutes.
In Phoenix and Las Vegas in summer, take the first departure. The gap between the 5am to 8am window and the 5pm to 8pm window was 22.4 points at Phoenix and 23.9 at Las Vegas. If a morning is impossible, compare the late-night window: out of Las Vegas it ran 72.0% against 66.9% for early evening.
At Denver in winter, fly early for the rebooking room, not the on-time odds. Snow shows up in cancellations, and a cancelled 7am leaves the rest of the day to find a seat. A cancelled 7pm often means a hotel. For trips onward to the mountains, the ski country guide covers the small-field leg.
On Southwest at these three airports, the morning flight is the product to buy. The same fare at 6pm is a different risk.
Albuquerque is the quiet alternative for New Mexico trips: 83.1% on time and a cancellation rate of 0.86%. Its weakest window is the late-night one (8pm–5am, 63.1%), so it is not the airport for a midnight departure.
Compare the fields: Salt Lake City (SLC) · Denver (DEN) · Phoenix (PHX) · Las Vegas (LAS) · Albuquerque (ABQ) · Compare any US route