Route reliability record
DEN→STL
Denver to St. Louis
- Flights
- 3,699
- Period
- September 2025 to August 2026
- Distance
- 770 mi
- Carriers
- 4
This route lands a B+, level with the national rate of 77.3%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 3,699 DEN to STL flights, of which United Airlines flew 1,116 at 78.0% on time.
Best time to fly DEN to STL: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 94.6% of the time and Tuesday flights 83.2%, against 77.7% for the route overall.
The US average over the same twelve months is 77.3%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
77.7%
Arrivals under 15 minutes late, of 3,674 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
0.49%
National rate is 1.89%
Best carrier
United
78.0% on time across 1,116 flights
These figures cover 3,699 flights between September 2025 and August 2026. The median arrival is 6 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 DEN to STL
The two carriers here are closely matched: about a point separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SkyWest Airlinesthin sample | 88 | 83.7% | 100 min | 1.14% | B |
| Frontier Airlinesthin sample | 292 | 82.5% | 53 min | 0.34% | B+ |
| United Airlines | 1,116 | 78.0% | 67 min | 0.36% | B+ |
| Southwest Airlines | 2,203 | 76.6% | 59 min | 0.54% | B+ |
No carrier stands out. United tops the table at 78.0%, about a point clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Flights on DEN 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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Best ways to make this trip
The most reliable ways to fly Denver to St. Louis
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. DEN → STLDenver to St. Louis | United Airlines | 77.7% | 78.0% | 0.36% | 11am–2pm, Tue | UA 652 09:35 |
| 2. DEN → STLDenver to St. Louis | Southwest Airlines | 76.2% | 76.6% | 0.54% | 5am–8am, Tue | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 32 points, against about a point between the best and worst carrier.
- 5am–8am634 flights94.6%
- 8am–11am789 flights87.7%
- 11am–2pm590 flights83.1%
- 2pm–5pm505 flights70.0%
- 5pm–8pm763 flights62.5%
- 8pm–5am418 flights62.3%
Scale runs 55% to 100%.
The 8pm–5am window is where this operation falls apart: 62.3% on time, against 94.6% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 8am–11am window is the busiest, with 789 flights scheduled in it.
Explore
Filter DEN 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 DEN to STL, the best departure window is 5am–8am at 94.6% on time and the worst is 8pm–5am at 62.3%, a wide gap of 32.3 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am94.6%
- 8–11am87.7%
- 11am–2pm83.1%
- 2–5pm70.0%
- 5–8pm62.5%
- 8pm–5am62.3%
best all US flightsScale 55% to 100%.
Across the year
When delays peak on this route
This route's year swings by 22 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 66.1% on time, 22 points below February, the best at 87.7%. 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 385 flights.
Across the week, Tuesday is the strongest day at 83.2% on time and Monday the weakest at 74.0%, a spread of 9 points.
Delay causes
Why this route gets delayed
Late-arriving aircraft accounts for 56% of the 50,000 delay minutes carriers reported here, and the remaining four split what is left.
- 56%Late-arriving aircraft
- 28%Carrier
- 13%National Airspace System
- 3%Extreme weather
- 0%Security
56% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 50,000 reported delay minutes here, that single category outweighs weather by 19 to one. The split is drawn from 50,378 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 94.6% on time here.
Cancellations are rare at 0.49%, 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
7.9% 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 770 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 runs 75.0% on time across 3,687 flights, within 3 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
The sample behind these figures is 3,699 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in STL after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 87.7% on time and August 66.1%, a swing of 22 points. If the dates move at all, move them out of August before you think about anything else. 3,674 completed flights over 12 months sit behind that.
Common questions
DEN to STL questions
How often is DEN to STL delayed?
Roughly one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.3% of the 3,699 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on DEN to STL?
United Airlines leads at 78.0% on time across 1,116 flights. Southwest Airlines is at the other end on 76.6%, a gap of about a point. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on DEN to STL?
The 5am–8am departure window is the strongest at 94.6% on time. The 8pm–5am window is the weakest at 62.3%, 32 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 DEN to STL?
August is the weakest month at 66.1% on time, compared with 87.7% in February. Across the year that is 22 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 DEN — the return legseparate record
- Denver International (DEN) delay statistics
- St. Louis Lambert International (STL) delay statistics
- Frontier Airlines on DEN to STL82.5%
- United Airlines on DEN to STL78.0%
- Southwest Airlines on DEN to STL76.6%
- DEN to PHX, a related route75.6%
- ATL to STL, a related route81.8%
- DEN to SLC, a related route78.2%
- SkyWest Airlines on-time record83.7%
- Frontier Airlines on-time record82.5%
- United Airlines on-time record78.0%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. DEN to STL and STL to DEN 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.