Route reliability record
DEN→ONT
Denver to Ontario
- Flights
- 2,623
- Period
- September 2025 to August 2026
- Distance
- 819 mi
- Carriers
- 3
This route sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.3%. The late ones land about an hour behind schedule. That rests on 2,623 DEN to ONT flights, of which Frontier Airlines flew 557 at 80.3% on time.
Best time to fly DEN to ONT: a 8am–11am departure, ideally on a Tuesday. Flights in that window arrived on time 90.4% of the time and Tuesday flights 78.9%, against 74.8% for the route overall.
Frontier Airlines is the most reliable of the three carriers covered here at 80.3% on time across 557 flights.
Key figures
On time
74.8%
Arrivals under 15 minutes late, of 2,617 completed flights
Avg delay
57 min
Across delayed arrivals only, not all flights
Cancelled
0.19%
National rate is 1.89%
Best carrier
Frontier
80.3% on time across 557 flights
These figures cover 2,623 flights between September 2025 and August 2026. Beyond the headline rate, 8.3% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Which airline is most reliable on DEN to ONT
The choice of carrier is not cosmetic here. Frontier Airlines arrives on time 80.3% of the time; Southwest Airlines manages 69.5%. Sample sizes sit next to every figure, because a two-point gap across 1,269 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Frontier Airlines | 557 | 80.3% | 61 min | 0.54% | B+ |
| United Airlines | 797 | 79.4% | 68 min | 0.00% | B+ |
| Southwest Airlines | 1,269 | 69.5% | 51 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
Flights on DEN to ONT
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly Denver to Ontario
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 4 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. DEN → SNADenver to Santa Ana | United Airlines | 85.2% | 85.3% | 0.16% | 5am–8am, Tue | UA 2666 07:40 |
| 2. DEN → LAXDenver to Los Angeles | United Airlines | 84.0% | 84.0% | 0.00% | 5am–8am, Sat | UA 1638 08:00 |
| 3. DEN → LAXDenver to Los Angeles | Frontier Airlines | 82.8% | 83.4% | 0.75% | 5am–8am, Sun | F9 2341 06:00 |
| 4. DEN → LAXDenver to Los Angeles | Delta Air Lines | 80.1% | 81.2% | 1.34% | 5am–8am, Mon | DL 2002 07:25 |
| 5. DEN → ONTDenver to Ontario | Frontier Airlines | 79.9% | 80.3% | 0.54% | 5am–8am, Sun | F9 1261 22:29 |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 27 points, against 11 points between the best and worst carrier.
- 5am–8am65 flights89.2%
- 8am–11am502 flights90.4%
- 11am–2pm642 flights82.5%
- 2pm–5pm143 flights73.2%
- 5pm–8pm609 flights65.0%
- 8pm–5am662 flights63.2%
Scale runs 55% to 95%.
The 8pm–5am window is where this operation falls apart: 63.2% on time, against 90.4% for the 8am–11am 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 8pm–5am window is the busiest, with 662 flights scheduled in it.
Explore
Filter DEN to ONT by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On DEN to ONT, the best departure window is 8am–11am at 90.4% on time and the worst is 8pm–5am at 63.2%, a wide gap of 27.2 points. All US flights leaving 8am–11am ran 83.9%.
- 5–8am89.2%
- 8–11am90.4%
- 11am–2pm82.5%
- 2–5pm73.2%
- 5–8pm65.0%
- 8pm–5am63.2%
best all US flightsScale 55% to 95%.
Across the year
When delays peak on this route
This route's year swings by 28 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
June is the worst month at 55.8% on time, 28 points below November, the best at 83.6%. 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. June was the busiest month here, with 250 flights.
Across the week, Tuesday is the strongest day at 78.9% on time and Monday the weakest at 69.7%, a spread of 9 points.
Delay causes
Why this route gets delayed
Late-arriving aircraft accounts for 55% of the 38,000 delay minutes carriers reported here, and the remaining four split what is left.
- 55%Late-arriving aircraft
- 35%Carrier
- 9%National Airspace System
- 1%Extreme weather
- 0%Security
55% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 38,000 reported delay minutes here, that single category outweighs weather by 55 to one. The split is drawn from 37,709 reported delay minutes.
The largest share of delay minutes, 35%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 13,000 of the 38,000 delay minutes reported here.
Cancellations are rare at 0.19%, below the national 1.89% 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 actually costs
8.3% of arrivals land an hour or more late, close to the national 8.3%, so 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.
The return leg is a different operation and performs like one: it runs 81.8% on time across 2,624 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.
The sample behind these figures is 2,623 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in ONT after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. November runs 83.6% on time and June 55.8%, a swing of 28 points. If the dates move at all, move them out of June before you think about anything else. 2,617 completed flights over 12 months sit behind that.
Common questions
DEN to ONT questions
How often is DEN to ONT delayed?
About one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 25.2% of the 2,623 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on DEN to ONT?
Frontier Airlines leads at 80.3% on time across 557 flights. Southwest Airlines is at the other end on 69.5%, a gap of 11 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on DEN to ONT?
The 8am–11am departure window is the strongest at 90.4% on time. The 8pm–5am window is the weakest at 63.2%, 27 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are June delays on DEN to ONT?
June is the weakest month at 55.8% on time, compared with 83.6% in November. Across the year that is 28 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- ONT to DEN — the return legseparate record
- Denver International (DEN) delay statistics
- Ontario International (ONT) delay statistics
- Frontier Airlines on DEN to ONT80.3%
- United Airlines on DEN to ONT79.4%
- Southwest Airlines on DEN to ONT69.5%
- DEN to PHX, a related route75.6%
- PHX to ONT, a related route76.8%
- DEN to SLC, a related route78.2%
- Frontier Airlines on-time record80.3%
- United Airlines on-time record79.4%
- Southwest Airlines on-time record69.5%
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
Direction matters. DEN to ONT and ONT to DEN are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.