Carrier route record
F9STL→DEN
Frontier Airlines · St. Louis to Denver
- Flights
- 277
- Period
- July 2025 to June 2026
- Share of route
- 8%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Frontier Airlines.
Frontier on STL to DEN sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.6%. The late ones land an hour and a half behind schedule. That rests on 277 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,071 at 76.6% on time.
The US average over the same twelve months is 77.6%, so there is little to separate Frontier on STL to DEN from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
74.5%
Arrivals under 15 minutes late, of 274 completed flights
Avg delay
83 min
Across delayed arrivals only, not all flights
Cancelled
1.08%
National rate is 1.81%
Whole route
74.9%
Every carrier on STL to DEN, 3,655 flights
These figures cover 277 flights between July 2025 and June 2026. Beyond the headline rate, 11.7% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Carrier by carrier
Frontier against every carrier on STL to DEN
Frontier flew 277 of the 3,655 flights on STL to DEN, about 8% of it. Its 74.5% on time is about level with the route as a whole at 74.9%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from SkyWest at 87.1% to Southwest at 73.3%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: 3 points 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 | 142 | 87.1% | 60 min | 0.70% | A+ |
| United Airlines | 1,071 | 76.6% | 91 min | 0.56% | B+ |
| Frontier Airlines (this page)thin sample | 277 | 74.5% | 83 min | 1.08% | C |
| Southwest Airlines | 2,165 | 73.3% | 60 min | 0.23% | C+ |
No carrier stands out. United tops the table at 76.6%, 3 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Frontier flight numbers on STL to DEN
Departure window
When Frontier runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 16 points, against 3 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am—
- 8am–11am—
- 11am–2pm5 flights—
- 2pm–5pm18 flights—
- 5pm–8pm100 flights63.3%
- 8pm–5am154 flights79.7%
Scale runs 55% to 85%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 63.3% on time, against 79.7% for the 8pm–5am 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 8pm–5am window is the busiest, with 154 flights scheduled in it.
Across the year
Frontier on STL to DEN through the year
- Jul–Sep 202571 flights71.4%
- Oct–Dec 202579 flights84.6%
- Jan–Mar 202653 flights71.7%
- Apr–Jun 202674 flights68.5%
Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.
Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 74.5% on time across 277 flights.
Frontier on STL to DEN did not run the same all year. Its best quarter was Oct–Dec 2025 at 84.6% on time and its weakest Apr–Jun 2026 at 68.5%, a swing of 16 points on roughly 69 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
Across the week, Wednesday is the strongest day at 80.4% on time and Friday the weakest at 56.9%. 24 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Frontier runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 54% of the 5,773 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.
- 54%Late-arriving aircraft
- 29%National Airspace System
- 16%Carrier
- 1%Extreme weather
54% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 5,773 reported delay minutes here, that single category outweighs weather by 54 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 5,773 reported delay minutes.
Cancellations sit at 1.08% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 11.7% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
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. 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 85.9% on time across 277 flights, 11 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 11 points of difference.
One caution: this is a thin sample. 277 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.
What to do with this
Booking Frontier on STL to DEN
Put together: treat all of this as provisional. 277 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 74.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 274 completed flights over 12 months sit behind that.
Related
Where to go next
- STL to DEN, every carrier
- Frontier on DEN to STL, the return leg
- SkyWest Airlines on STL to DEN87.1%
- United Airlines on STL to DEN76.6%
- Southwest Airlines on STL to DEN73.3%
- Frontier Airlines network-wide record
- St. Louis Lambert International (STL) delay statistics
- Denver International (DEN) delay statistics
- Why the first flight of the morning is statistically safest
- How often a connection fails at the major US hubs
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.