ONT to DEN flight delays
Ontario, CA (ONT) Denver, CO (DEN) · 819 miles
250 flights · March 2025 – August 2026 · US Bureau of Transportation Statistics
77.42%
Arrived on time
Within 15 minutes of schedule
0%
Cancelled
Share of scheduled flights
88 min
When late, late by
Average across delayed arrivals
21 min
Delay per flight
Averaged over every flight flown
What the record says about this route
The two directions do not behave alike. DEN to ONT arrives on time 21.6 points less often than the outbound. Delay accumulates through the flying day, so whichever direction is scheduled later tends to carry the worse record — which is an argument for booking the morning departure if the choice exists.
Only Southwest Airlines flies this route in the published record, so there is no choice to weigh — the route's figures and the airline's are the same figures.
This is a thin route — 250 flights across the whole period. On a route this infrequent a cancellation is far more costly than the rate suggests, because the next departure may not be the same day.
The Ontario to Denver route sits close to the middle of the record — neither notably punctual nor notably late.
Which airline should you fly on this route?
Over March 2025 – August 2026, Southwest Airlines arrived on time most often on ONT to DEN.
Every airline on ONT to DEN
Ranked by how many flights each one operated. A carrier with fewer than 100 flights in the period is listed but not graded.
| Airline | Flights | On time | Cancelled | Avg delay | Grade |
|---|---|---|---|---|---|
| Southwest Airlines | 114 | 66.96% | 0% | 50 min | D |
| United Airlines | 76 | 82.89% | 0% | 104 min | — |
| Frontier Airlines | 60 | 90% | 0% | 292 min | — |
The return leg
DEN to ONT Denver back to Ontario 55.82% on time FOther routes from Ontario
Common questions
Are flights from Ontario to Denver usually delayed?
77.42% of flights on the ONT to DEN route arrived within 15 minutes of schedule, so roughly 2 in every ten arrived late. That is about the same as the average route in this record.
Which airlines fly from Ontario to Denver?
Only Southwest Airlines appears in the published record on this route, with 114 flights and 66.96% arriving on time.
How often are ONT to DEN flights cancelled?
0% of scheduled flights did not operate — about 1 in every thousand. That is in the normal range.
When ONT to DEN flights are late, how late are they?
About 88 minutes on average across the flights that arrived more than 15 minutes behind schedule.
What these figures do and do not tell you
Everything on this page is counted from the flights that actually operated on ONT to DEN during March 2025 – August 2026, as reported by the airlines to the US Bureau of Transportation Statistics. "On time" is the federal definition: arriving at the gate within 15 minutes of the scheduled time.
A route's record is a description of the past, not a forecast. Weather, air traffic control and the aircraft's earlier flights that day drive most delays, and none of them are predictable from a historical rate. What the record does tell you is whether this route runs late more often than others, and which carrier on it has the better history — which is the part you can actually act on when you book.
Cancellations are counted separately from delays because they are a different problem for a traveller: a late flight still gets you there. How the grade is calculated →