ONT to DEN flight delays & on-time performance
Nonstop flights from Ontario International Airport to Denver International Airport · 819 miles · Aug 2025 – Jul 2026
No FAA-reported ground stops or delays at ONT or DEN right now. Individual flights can still be delayed by the airline; check with your airline for your flight.
Key facts
- Flights from Ontario (ONT) to Denver (DEN) arrived on time 81% of the time in Aug 2025 – Jul 2026, better than the 78% national average.
- 0.3% were cancelled, and 7% arrived an hour or more late.
- United Airlines was the most punctual airline here (87% on time); Southwest Airlines was the least (76%).
- Departures scheduled around 5am did best (95% on time); around 12pm did worst (56%).
- Sunday was the most reliable day to fly (84% on time) and Monday the least (79%).
- The largest source of delay minutes was late-arriving aircraft (40%).
Which airline is most on time from ONT to DEN?
Ranked by on-time arrival rate. Regional airlines fly under their partner's brand (e.g. SkyWest for Delta Connection or United Express).
| Airline | On time | Cancelled | Avg delay | 1 hr+ late | Flights |
|---|---|---|---|---|---|
| United Airlines | 87% | 0.4% | 12 min | 6.0% | 823 |
| Frontier Airlines | 84% | 0.4% | 16 min | 6.7% | 552 |
| Southwest Airlines | 76% | 0.3% | 14 min | 7.0% | 1,268 |
Best time of day to fly
On-time arrival rate by scheduled departure hour (local time).
- 12am81%69 flights
- 5am95%564 flights
- 6am88%352 flights
- 7am88%50 flights
- 8am93%194 flights
- 9am91%78 flights
- 10am82%143 flights
- 11am74%57 flights
- 12pm56%92 flights
- 1pm77%481 flights
- 2pm60%201 flights
- 3pm60%102 flights
- 4pm57%87 flights
- 5pm62%39 flights
- 6pm79%91 flights
- 8pm88%32 flights
Best day of the week
On-time arrival rate by day of departure.
- Monday79%0.0% cancelled
- Tuesday82%0.3% cancelled
- Wednesday79%0.0% cancelled
- Thursday81%0.2% cancelled
- Friday80%1.0% cancelled
- Saturday83%0.0% cancelled
- Sunday84%0.7% cancelled
On-time trend by month
Why flights are late
Share of delay minutes by cause, as reported by airlines to the DOT.
- Late-arriving aircraft40%
- Air traffic control & airport congestion33%
- Airline (crew, maintenance, cleaning, fueling)25%
- Extreme weather2%
- Security0%
Why flights are cancelled
Share of cancellations by reason.
- Airline (crew, maintenance, cleaning, fueling)67%
- Air traffic control & airport congestion22%
- Extreme weather11%
- Security0%
ONT to DEN: common questions
- How often are ONT to DEN flights on time?
- 81% of flights arrived less than 15 minutes late in Aug 2025 – Jul 2026, compared with 78% for all US flights.
- How often are flights from Ontario to Denver cancelled?
- 0.3% of scheduled flights were cancelled (9 of 2,643).
- How long are typical delays?
- Across all flights the average arrival delay was 14 min (early arrivals count as zero). Flights that were late arrived 68 min behind schedule on average, and 6.6% of flights were an hour or more late.
- How long is taxi time at ONT?
- Flights on this route spent 14 min taxiing from the gate to takeoff on average.
Related routes
Return trip: DEN to ONT — 75% on time
More flights from Ontario
Data: U.S. DOT Bureau of Transportation Statistics, Aug 2025 – Jul 2026 (12 months). Latest month published by BTS: July 2026. Route: ONT → DEN, nonstop flights by US airlines that report to the DOT. How we calculate this.