Carrier route record
UADEN→ONT
United Airlines · Denver to Ontario
- Flights
- 853
- Period
- July 2025 to June 2026
- Share of route
- 32%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.
United on DEN to ONT lands a B+, level with the national rate of 77.6%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 853 flights. The strongest carrier on the route with a full sample, Frontier Airlines, flew 551 at 79.1% on time.
The US average over the same twelve months is 77.6%, so there is little to separate United 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
77.9%
Arrivals under 15 minutes late, of 852 completed flights
Avg delay
68 min
Across delayed arrivals only, not all flights
Cancelled
0.00%
National rate is 1.81%
Whole route
73.4%
Every carrier on DEN to ONT, 2,671 flights
These figures cover 853 flights between July 2025 and June 2026. Beyond the headline rate, 8.6% 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
United against every carrier on DEN to ONT
United flew 853 of the 2,671 flights on DEN to ONT, about 32% of it. Its 77.9% on time is 5 points better than the route as a whole, which runs 73.4%. Ranked by on-time rate it is number two 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. Frontier Airlines arrives on time 79.1% 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 | 551 | 79.1% | 62 min | 0.36% | B+ |
| United Airlines (this page) | 853 | 77.9% | 68 min | 0.00% | B+ |
| Southwest Airlines | 1,267 | 68.0% | 49 min | 0.16% | C+ |
Frontier leads Southwest by 11 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
United flight numbers on DEN to ONT
Departure window
When United 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 11 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–2pm368 flights87.0%
- 2pm–5pm119 flights66.1%
- 5pm–8pm364 flights72.5%
- 8pm–5am2 flights—
Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 87.0% on time, ahead of 2pm–5pm at 66.1%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 11am–2pm window is the busiest, with 368 flights scheduled in it.
Across the year
United on DEN to ONT through the year
July is the worst month at 60.4% on time, 33 points below April, the best at 93.3%. 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 91 flights.
Across the week, Friday is the strongest day at 81.6% on time and Thursday the weakest at 73.6%. 8 points is a smaller lever than departure hour, but it is free.
Delay causes
Why United runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 57% of the 13,000 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.
- 57%Late-arriving aircraft
- 30%Carrier
- 12%National Airspace System
- 1%Extreme weather
57% 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 13,000 reported delay minutes here, that single category outweighs weather by 53 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 12,856 reported delay minutes.
Cancellations are rare at 0.00%, below the national 1.81% and low enough to earn the plus on the grade. Almost no flights are called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here costs
8.6% 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 a little over 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 is a different operation and performs like one: it runs 85.1% on time across 853 flights, 7 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 7 points of difference.
One caution: this is a thin sample. 853 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 United on DEN to ONT
Put together: treat all of this as provisional. 853 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 77.9% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 852 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to ONT, every carrier
- United on ONT to DEN, the return leg
- Frontier Airlines on DEN to ONT79.1%
- Southwest Airlines on DEN to ONT68.0%
- United Airlines network-wide record
- Denver International (DEN) delay statistics
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
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.