Route reliability record
STL→SLC
St. Louis to Salt Lake City
- Flights
- 990
- Period
- September 2025 to August 2026
- Distance
- 1,156 mi
- Carriers
- 2
This route earns an A+. More than four flights in five 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 77.3%. When something does go wrong the average delay runs close to two hours. That rests on 990 STL to SLC flights, with a median arrival 8 minutes early.
Best time to fly STL to SLC: a 8am–11am departure, ideally on a Friday. Flights in that window arrived on time 95.3% of the time and Friday flights 90.3%, against 86.8% for the route overall.
Set against the rest of the country, this route's record is 10 points better than the US average of 77.3%. That gap is worth roughly 95 fewer late arrivals for every thousand flights.
Key figures
On time
86.8%
Arrivals under 15 minutes late, of 979 completed flights
Avg delay
102 min
Across delayed arrivals only, not all flights
Cancelled
0.91%
National rate is 1.89%
Best carrier
Delta
87.0% 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 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 |
|---|---|---|---|---|---|
| Delta Air Lines | 981 | 87.0% | 103 min | 0.92% | A+ |
| Southwest Airlinesthin sample | 9 | 66.7% | 40 min | 0.00% | C+ |
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.
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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 14 points, against half a point between the best and worst carrier.
- 5am–8am279 flights89.9%
- 8am–11am86 flights95.3%
- 11am–2pm8 flights—
- 2pm–5pm304 flights86.3%
- 5pm–8pm223 flights83.1%
- 8pm–5am90 flights81.1%
Scale runs 75% to 100%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 95.3% of the time, against 81.1% for the overnight window. That is 14 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 304 flights scheduled in it.
Explore
Filter STL to SLC 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 STL to SLC, the best departure window is 8am–11am at 95.3% on time and the worst is 8pm–5am at 81.1%, a wide gap of 14.2 points. All US flights leaving 8am–11am ran 83.9%.
- 5–8am89.9%
- 8–11am95.3%
- 11am–2pm—
- 2–5pm86.3%
- 5–8pm83.1%
- 8pm–5am81.1%
best all US flightsScale 60% to 100%. Cells under 30 flights show a dash.
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 93 flights.
Across the week, Friday is the strongest day at 90.3% on time and Saturday the weakest at 81.4%, a spread of 9 points.
Delay causes
Why this route gets delayed
Carrier accounts for 60% of the 13,000 delay minutes carriers reported here, and the remaining four split what is left.
- 60%Carrier
- 25%Late-arriving aircraft
- 8%Extreme weather
- 7%National Airspace System
- 0%Security
The largest share of delay minutes, 60%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 7,859 of the 13,000 delay minutes reported here. The split is drawn from 13,092 reported delay minutes.
Cancellations sit at 0.91% against a national 1.89%, which is ordinary. Diversions add another 0.20%.
Connections and stage length
What a delay here actually costs
5.5% 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 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.
The return leg is a different operation and performs like one: it runs 83.7% on time across 990 flights, 3 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 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 SLC 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 86.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 979 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 13.2% of the 990 flights in this analysis, against 22.7% 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?
86.8% of flights arrive on time here against a national 77.3%, 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 8am–11am departure window is the strongest at 95.3% on time. The 8pm–5am window is the weakest at 81.1%, 14 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 DEN, a related route75.0%
- DEN to SLC, a related route78.2%
- STL to ATL, a related route84.6%
- Delta Air Lines on-time record87.0%
- Southwest Airlines on-time record66.7%
- 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. 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.
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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.