Carrier route record
F9ONT→DEN
Frontier Airlines · Ontario to Denver
- Flights
- 552
- Period
- July 2025 to June 2026
- Share of route
- 21%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Frontier Airlines.
Frontier on ONT to DEN lands a B+, 3 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 552 flights. The strongest carrier on the route with a full sample, United Airlines, flew 853 at 85.1% on time.
The US average over the same twelve months is 77.6%, so there is little to separate Frontier on ONT 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
80.1%
Arrivals under 15 minutes late, of 548 completed flights
Avg delay
98 min
Across delayed arrivals only, not all flights
Cancelled
0.72%
National rate is 1.81%
Whole route
79.7%
Every carrier on ONT to DEN, 2,672 flights
These figures cover 552 flights between July 2025 and June 2026. Beyond the headline rate, 9.9% 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 ONT to DEN
Frontier flew 552 of the 2,672 flights on ONT to DEN, about 21% of it. Its 80.1% on time is about level with the route as a whole at 79.7%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from United at 85.1% to Southwest at 75.9%.
The choice of carrier is not cosmetic here. United Airlines arrives on time 85.1% of the time; Southwest Airlines manages 75.9%. Sample sizes sit next to every figure, because a two-point gap across 1,267 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 853 | 85.1% | 85 min | 0.35% | A+ |
| Frontier Airlines (this page) | 552 | 80.1% | 98 min | 0.72% | B+ |
| Southwest Airlines | 1,267 | 75.9% | 53 min | 0.39% | B+ |
United leads Southwest by 9 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Frontier flight numbers on ONT 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 36 points, against 9 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am205 flights90.2%
- 8am–11am73 flights84.9%
- 11am–2pm19 flights—
- 2pm–5pm45 flights70.5%
- 5pm–8pm78 flights54.5%
- 8pm–5am132 flights80.2%
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 54.5% on time, against 90.2% 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 5am–8am window is the busiest, with 205 flights scheduled in it.
Across the year
Frontier on ONT to DEN through the year
July is the worst month at 53.3% on time, 40 points below January, the best at 93.5%. 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 62 flights.
Across the week, Thursday is the strongest day at 84.4% on time and Monday the weakest at 73.8%. 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. Late-arriving aircraft accounts for 46% of the 11,000 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.
- 46%Late-arriving aircraft
- 27%Carrier
- 27%National Airspace System
- 0%Extreme weather
46% 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 11,000 reported delay minutes here, that single category outweighs weather by 46 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 10,725 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 90.2% on time here.
Cancellations are rare at 0.72%, 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
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.9% 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 819 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 runs 79.1% on time across 551 flights, within about a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
One caution: this is a thin sample. 552 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 ONT to DEN
Put together: treat all of this as provisional. 552 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 80.1% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 548 completed flights over 12 months sit behind that.
Related
Where to go next
- ONT to DEN, every carrier
- Frontier on DEN to ONT, the return leg
- United Airlines on ONT to DEN85.1%
- Southwest Airlines on ONT to DEN75.9%
- Frontier Airlines network-wide record
- 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.