Route reliability record
SLC→STL
Salt Lake City to St. Louis
- Flights
- 989
- Period
- July 2025 to June 2026
- Distance
- 1,156 mi
- Carriers
- 3
This route lands a B+, 6 points better than the national rate of 77.6%. About one flight in six arrives 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 989 SLC to STL flights, with a median arrival 10 minutes early.
Best time to fly SLC to STL: a 11am–2pm departure, ideally on a Wednesday. Flights in that window arrived on time 90.1% of the time and Wednesday flights 89.6%, against 83.9% for the route overall.
Set against the rest of the country, this route's record is 6 points better than the US average of 77.6%. That gap is worth roughly 63 fewer late arrivals for every thousand flights.
Key figures
On time
83.9%
Arrivals under 15 minutes late, of 981 completed flights
Avg delay
63 min
Across delayed arrivals only, not all flights
Cancelled
0.51%
National rate is 1.81%
Best carrier
Delta
83.8% on time across 978 flights
These figures cover 989 flights between July 2025 and June 2026. The median arrival is 10 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 STL
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+ |
| Southwest Airlinesthin sample | 9 | 88.9% | 54 min | 0.00% | A+ |
| Delta Air Lines | 978 | 83.8% | 63 min | 0.51% | B+ |
Flight by flight
Flights on SLC to STL
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 matters more here than the choice of carrier. The gap between the best and worst window is 13 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am—
- 8am–11am342 flights89.9%
- 11am–2pm83 flights90.1%
- 2pm–5pm200 flights81.4%
- 5pm–8pm99 flights80.6%
- 8pm–5am265 flights77.4%
Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 90.1% on time, ahead of 8pm–5am at 77.4%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 8am–11am window is the busiest, with 342 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 16 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.
Delays peak in September, when the on-time rate falls to 77.8%. March is the strongest month at 94.2%. Moving a flexible trip across that boundary buys 16 points. July was the busiest month here, with 92 flights.
Across the week, Wednesday is the strongest day at 89.6% on time and Sunday the weakest at 75.9%. 14 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 65% of the 9,961 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.
- 65%Carrier
- 26%Late-arriving aircraft
- 8%National Airspace System
- 1%Extreme weather
The largest share of delay minutes, 65%, 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 6,425 of the 9,961 delay minutes reported here. The split is drawn from 9,961 reported delay minutes.
Cancellations are rare at 0.51%, 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
5.7% 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 last about an hour, 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 87.5% on time across 989 flights, 4 points above 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 STL 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 83.9% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 981 completed flights over 12 months sit behind that.
Common questions
SLC to STL questions
How often is SLC to STL delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 16.1% of the 989 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is SLC to STL compared with the rest of the country?
83.9% of flights arrive on time here against a national 77.6%, a difference of 6 points in its favour. That is worth a B+ on this site's grading scale.
What time of day has the fewest delays on SLC to STL?
The 11am–2pm departure window is the strongest at 90.1% on time. The 8pm–5am window is the weakest at 77.4%, 13 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 September delays on SLC to STL?
September is the weakest month at 77.8% on time, compared with 94.2% in March. Across the year that is 16 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
- STL to SLC — the return legseparate record
- Salt Lake City International (SLC) delay statistics
- St. Louis Lambert International (STL) delay statistics
- SLC to DEN, a related route77.8%
- ATL to STL, a related route82.4%
- SLC to PHX, a related route83.9%
- SkyWest Airlines on-time record100.0%
- Southwest Airlines on-time record88.9%
- Delta Air Lines on-time record83.8%
- 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. SLC to STL and STL to SLC are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.