Carrier route record

F9DEN→STL

Frontier Airlines · Denver to St. Louis

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 DEN to STL 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 8 points better than the national rate of 77.6%. When something does go wrong the average delay runs roughly 45 minutes. That rests on 277 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,072 at 79.5% on time.

Set against the rest of the country, Frontier's DEN to STL record is 8 points better than the US average of 77.6%. That gap is worth roughly 83 fewer late arrivals for every thousand flights.

On time

85.9%

Arrivals under 15 minutes late, of 276 completed flights

Avg delay

47 min

Across delayed arrivals only, not all flights

Cancelled

0.36%

National rate is 1.81%

Whole route

78.1%

Every carrier on DEN to STL, 3,662 flights

These figures cover 277 flights between July 2025 and June 2026. The median arrival is 14 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

Frontier against every carrier on DEN to STL

Frontier flew 277 of the 3,662 flights on DEN to STL, about 8% of it. Its 85.9% on time is 8 points better than the route as a whole, which runs 78.1%. Ranked by on-time rate it is first of four carriers on the route, where the range runs from Frontier at 85.9% to Southwest at 76.4%. 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.

On-time performance by carrier on DEN to STL
Airline	Flights	On time	Avg delay	Cancelled	Grade
Frontier Airlines (this page)thin sample	277	85.9%	47 min	0.36%	A+
United Airlines	1,072	79.5%	62 min	0.28%	B+
SkyWest Airlinesthin sample	141	77.0%	52 min	0.71%	B+
Southwest Airlines	2,172	76.4%	58 min	0.41%	B+

No carrier stands out. United tops the table at 79.5%, 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 DEN to STL

F9 330206:0085.9% · 277 flights

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 21 points, against 3 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am175 flights91.4%
8am–11am15 flights—
11am–2pm11 flights—
2pm–5pm76 flights70.7%
5pm–8pm—
8pm–5am—

Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 91.4% of the time, against 70.7% for the afternoon window. That is 21 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 175 flights scheduled in it.

Across the year

Frontier on DEN to STL through the year

Jul–Sep 202571 flights88.7%
Oct–Dec 202579 flights93.7%
Jan–Mar 202653 flights90.6%
Apr–Jun 202674 flights71.2%

Scale runs 65% to 100%. 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 85.9% on time across 277 flights.

Frontier on DEN to STL did not run the same all year. Its best quarter was Oct–Dec 2025 at 93.7% on time and its weakest Apr–Jun 2026 at 71.2%, a swing of 23 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 93.5% on time and Friday the weakest at 82.7%. 11 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. Carrier accounts for 43% of the 1,816 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.

Carrier
43%
Late-arriving aircraft
27%
National Airspace System
23%
Extreme weather
7%

The largest share of delay minutes, 43%, 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 789 of the 1,816 delay minutes reported here. The split is drawn from 1,816 reported delay minutes.

Cancellations are rare at 0.36%, 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 costs

Badly late arrivals are rare here: only 2.2% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

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 74.5% on time across 277 flights, 11 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 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 DEN to STL

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 85.9% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 276 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures