Carrier route record
F9DEN→ONT
Frontier Airlines · Denver to Ontario
- Flights
- 551
- 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 DEN to ONT lands a B+, 2 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 about an hour on average. That is a workable record, not a spotless one. That rests on 551 flights. The strongest carrier on the route with a full sample, United Airlines, flew 853 at 77.9% on time.
The US average over the same twelve months is 77.6%, so there is little to separate Frontier on DEN to ONT from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
79.1%
Arrivals under 15 minutes late, of 549 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
0.36%
National rate is 1.81%
Whole route
73.4%
Every carrier on DEN to ONT, 2,671 flights
These figures cover 551 flights between July 2025 and June 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.
Carrier by carrier
Frontier against every carrier on DEN to ONT
Frontier flew 551 of the 2,671 flights on DEN to ONT, about 21% of it. Its 79.1% on time is 6 points better than the route as a whole, which runs 73.4%. Ranked by on-time rate it is first of three carriers on the route, where the range runs from Frontier at 79.1% to Southwest at 68.0%.
The choice of carrier is not cosmetic here. United Airlines arrives on time 77.9% of the time; Southwest Airlines manages 68.0%. 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 |
|---|---|---|---|---|---|
| Frontier Airlines (this page) | 551 | 79.1% | 62 min | 0.36% | B+ |
| United Airlines | 853 | 77.9% | 68 min | 0.00% | B+ |
| Southwest Airlines | 1,267 | 68.0% | 49 min | 0.16% | C+ |
United leads Southwest by 10 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Frontier flight numbers on DEN to ONT
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 23 points, against 10 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am85 flights92.9%
- 8am–11am104 flights89.4%
- 11am–2pm14 flights—
- 2pm–5pm3 flights—
- 5pm–8pm34 flights85.3%
- 8pm–5am311 flights69.9%
Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 92.9% of the time, against 69.9% for the overnight window. That is 23 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8pm–5am window is the busiest, with 311 flights scheduled in it.
Across the year
Frontier on DEN to ONT through the year
June is the worst month at 70.0% on time, 20 points below April, the best at 89.7%. 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 62 flights.
Across the week, Wednesday is the strongest day at 84.6% on time and Monday the weakest at 69.4%. 15 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 48% of the 7,172 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.
- 48%Carrier
- 41%Late-arriving aircraft
- 9%National Airspace System
- 2%Extreme weather
41% 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 7,172 reported delay minutes here, that single category outweighs weather by 24 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 7,172 reported delay minutes.
The largest share of delay minutes, 48%, 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 3,455 of the 7,172 delay minutes reported here.
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
7.5% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says 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 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 80.1% on time across 552 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. 551 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 ONT
Put together: treat all of this as provisional. 551 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 79.1% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 549 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to ONT, every carrier
- Frontier on ONT to DEN, the return leg
- United Airlines on DEN to ONT77.9%
- Southwest Airlines on DEN to ONT68.0%
- Frontier Airlines network-wide record
- Denver International (DEN) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.