Route reliability record
STL→SLC
St. Louis to Salt Lake City
- Flights
- 989
- Period
- July 2025 to June 2026
- Distance
- 1,156 mi
- Carriers
- 3
This route earns an A+. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 10 points better than the national rate of 77.6%. When something does go wrong the average delay runs close to two hours. That rests on 989 STL to SLC flights, with a median arrival 9 minutes early.
Best time to fly STL to SLC: a 5am–8am departure, ideally on a Thursday. Flights in that window arrived on time 90.6% of the time and Thursday flights 91.0%, against 87.5% for the route overall.
Set against the rest of the country, this route's record is 10 points better than the US average of 77.6%. That gap is worth roughly 99 fewer late arrivals for every thousand flights.
Key figures
On time
87.5%
Arrivals under 15 minutes late, of 978 completed flights
Avg delay
103 min
Across delayed arrivals only, not all flights
Cancelled
0.81%
National rate is 1.81%
Best carrier
Delta
87.6% on time across 978 flights
These figures cover 989 flights between July 2025 and June 2026. The median arrival is 9 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 STL to SLC
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SkyWest Airlinesthin sample | 2 | 100.0% | — | 0.00% | A+ |
| Delta Air Lines | 978 | 87.6% | 104 min | 0.82% | A+ |
| Southwest Airlinesthin sample | 9 | 77.8% | 45 min | 0.00% | B+ |
Flight by flight
Flights on STL to SLC
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
Departure window
The best time of day to leave
Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 989 flights.
- 5am–8am341 flights90.6%
- 8am–11am24 flights—
- 11am–2pm4 flights—
- 2pm–5pm307 flights87.2%
- 5pm–8pm251 flights84.9%
- 8pm–5am62 flights82.3%
Scale runs 75% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 90.6% of the time, against 82.3% for the overnight window. That is 8 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 341 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 18 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.
February is the weak month at 76.9% on time, against 95.3% in May. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. July was the busiest month here, with 92 flights.
Across the week, Thursday is the strongest day at 91.0% on time and Saturday the weakest at 81.4%. 10 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. Carrier accounts for 57% of the 13,000 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.
- 57%Carrier
- 26%Late-arriving aircraft
- 10%Extreme weather
- 7%National Airspace System
The largest share of delay minutes, 57%, 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 7,167 of the 13,000 delay minutes reported here. The split is drawn from 12,526 reported delay minutes.
Cancellations are rare at 0.81%, 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
5.2% 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 close to two hours, which a normal layover absorbs.
The 1,156 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 is a different operation and performs like one: it runs 83.9% on time across 989 flights, 4 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 4 points of difference.
One caution: this is a thin sample. 989 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.
Work out the risk of missing a connection in SLC after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 989 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 87.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 978 completed flights over 12 months sit behind that.
Common questions
STL to SLC questions
How often is STL to SLC delayed?
About one flight in eight arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 12.5% of the 989 flights in this analysis, against 22.4% nationally. Delayed flights are late by close to two hours on average.
How reliable is STL to SLC compared with the rest of the country?
87.5% of flights arrive on time here against a national 77.6%, a difference of 10 points in its favour. That is worth a A+ on this site's grading scale.
What time of day has the fewest delays on STL to SLC?
The 5am–8am departure window is the strongest at 90.6% on time. The 8pm–5am window is the weakest at 82.3%, 8 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 February delays on STL to SLC?
February is the weakest month at 76.9% on time, compared with 95.3% in May. Across the year that is 18 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- SLC to STL — the return legseparate record
- St. Louis Lambert International (STL) delay statistics
- Salt Lake City International (SLC) delay statistics
- STL to ATL, a related route85.3%
- DEN to SLC, a related route77.5%
- STL to DEN, a related route74.9%
- SkyWest Airlines on-time record100.0%
- Delta Air Lines on-time record87.6%
- Southwest Airlines on-time record77.8%
- The best time of day to fly, according to 7.04 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. STL to SLC and SLC to STL are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Embed STL to SLC’s on-time badge on your site
Paste this into a web page. The badge shows the current on-time rate, cancellation rate and grade, and updates every month. Preview it, or build a badge for another route or airport.
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.