Carrier route record
UAONT→DEN
United Airlines · Ontario to Denver
- 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 ONT to DEN 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 an hour and a half. That rests on 853 flights. The strongest carrier on the route with a full sample, Frontier Airlines, flew 552 at 80.1% on time.
Set against the rest of the country, United's ONT to DEN record is 8 points better than the US average of 77.6%. That gap is worth roughly 75 fewer late arrivals for every thousand flights.
Key figures
On time
85.1%
Arrivals under 15 minutes late, of 846 completed flights
Avg delay
85 min
Across delayed arrivals only, not all flights
Cancelled
0.35%
National rate is 1.81%
Whole route
79.7%
Every carrier on ONT to DEN, 2,672 flights
These figures cover 853 flights between July 2025 and June 2026. The median arrival is 11 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
United against every carrier on ONT to DEN
United flew 853 of the 2,672 flights on ONT to DEN, about 32% of it. Its 85.1% on time is 5 points better than the route as a whole, which runs 79.7%. Ranked by on-time rate it is first of three carriers on the route, where the range runs from United at 85.1% to Southwest at 75.9%.
The two carriers here are closely matched: 4 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 |
|---|---|---|---|---|---|
| United Airlines (this page) | 853 | 85.1% | 85 min | 0.35% | A+ |
| Frontier Airlines | 552 | 80.1% | 98 min | 0.72% | B+ |
| Southwest Airlines | 1,267 | 75.9% | 53 min | 0.39% | B+ |
No carrier stands out. Frontier tops the table at 80.1%, 4 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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 20 points, against 4 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am364 flights93.6%
- 8am–11am—
- 11am–2pm340 flights81.3%
- 2pm–5pm28 flights—
- 5pm–8pm119 flights73.7%
- 8pm–5am2 flights—
Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 93.6% of the time, against 73.7% for the evening window. That is 20 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 364 flights scheduled in it.
Across the year
United on ONT to DEN through the year
July is the worst month at 65.2% on time, 33 points below April, the best at 98.3%. 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, Sunday is the strongest day at 90.2% on time and Thursday the weakest at 81.5%. 9 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 50% 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.
- 50%Late-arriving aircraft
- 26%National Airspace System
- 22%Carrier
- 1%Extreme weather
50% 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 37 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 10,741 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 93.6% on time here.
Cancellations are rare at 0.35%, 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
6.5% 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 an hour and a half, 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 77.9% on time across 853 flights, 7 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 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 ONT to DEN
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 85.1% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 846 completed flights over 12 months sit behind that.
Related
Where to go next
- ONT to DEN, every carrier
- United on DEN to ONT, the return leg
- Frontier Airlines on ONT to DEN80.1%
- Southwest Airlines on ONT to DEN75.9%
- United 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.