Route reliability record
SLC→STL
Salt Lake City to St. Louis
- Flights
- 990
- Period
- September 2025 to August 2026
- Distance
- 1,156 mi
- Carriers
- 2
This route lands a B+, 6 points better than the national rate of 77.3%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 990 SLC to STL flights, with a median arrival 8 minutes early.
Best time to fly SLC to STL: a 8am–11am departure, ideally on a Wednesday. Flights in that window arrived on time 89.3% of the time and Wednesday flights 89.6%, against 83.7% for the route overall.
Set against the rest of the country, this route's record is 6 points better than the US average of 77.3%. That gap is worth roughly 64 fewer late arrivals for every thousand flights.
Key figures
On time
83.7%
Arrivals under 15 minutes late, of 981 completed flights
Avg delay
58 min
Across delayed arrivals only, not all flights
Cancelled
0.61%
National rate is 1.89%
Best carrier
Delta
83.7% on time across 981 flights
These figures cover 990 flights between September 2025 and August 2026. The median arrival is 8 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.
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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 |
|---|---|---|---|---|---|
| Delta Air Lines | 981 | 83.7% | 58 min | 0.61% | B+ |
| Southwest Airlinesthin sample | 9 | 77.8% | 43 min | 0.00% | 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.
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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 11 points, against half a point between the best and worst carrier.
- 5am–8am1 flights—
- 8am–11am342 flights89.3%
- 11am–2pm82 flights88.8%
- 2pm–5pm201 flights79.5%
- 5pm–8pm102 flights82.2%
- 8pm–5am262 flights78.5%
Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 89.3% of the time, against 78.5% for the overnight window. That is 11 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 342 flights scheduled in it.
Explore
Filter SLC to STL by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On SLC to STL, the best departure window is 8am–11am at 89.3% on time and the worst is 8pm–5am at 78.5%, a wide gap of 10.8 points. All US flights leaving 8am–11am ran 83.9%.
- 5–8am—
- 8–11am89.3%
- 11am–2pm88.8%
- 2–5pm79.5%
- 5–8pm82.2%
- 8pm–5am78.5%
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 23 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.
August is the worst month at 71.6% on time, 23 points below March, the best at 94.2%. 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 93 flights.
Across the week, Wednesday is the strongest day at 89.6% on time and Sunday the weakest at 78.7%, a spread of 11 points.
Delay causes
Why this route gets delayed
Carrier accounts for 64% of the 9,252 delay minutes carriers reported here, and the remaining four split what is left.
- 64%Carrier
- 25%Late-arriving aircraft
- 9%National Airspace System
- 2%Extreme weather
The largest share of delay minutes, 64%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 5,941 of the 9,252 delay minutes reported here. The split is drawn from 9,252 reported delay minutes.
Cancellations are rare at 0.61%, below the national 1.89% 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
5.8% of arrivals land an hour or more late, close to the national 8.3%, so 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.
The return leg is a different operation and performs like one: it runs 86.8% on time across 990 flights, 3 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 3 points of difference.
One caution: this is a thin sample. 990 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. 990 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 83.7% 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 16.3% of the 990 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
How reliable is SLC to STL compared with the rest of the country?
83.7% of flights arrive on time here against a national 77.3%, 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 8am–11am departure window is the strongest at 89.3% on time. The 8pm–5am window is the weakest at 78.5%, 11 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 August delays on SLC to STL?
August is the weakest month at 71.6% on time, compared with 94.2% in March. Across the year that is 23 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 route79.0%
- DEN to STL, a related route77.7%
- SLC to PHX, a related route83.5%
- Delta Air Lines on-time record83.7%
- Southwest Airlines on-time record77.8%
- The best time of day to fly, according to 7.05 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.