Ontario (ONT) to Denver (DEN): On-Time Performance
Data through July 2026
Ontario (ONT) to Denver (DEN) effectively runs on two schedules. In September 2024, 90% of arrivals were on time; in July 2025 that fell to 65% — a 26-point seasonal swing. Across the full period the route averages 81% on-time against a national 78%. Morning departures also hold up better than evening ones (91% vs 72%), which matters most in the rough months.
- On-time
- 81%
- arrived <15 min late
- Avg delay
- 14 min
- completed flights
- Cancelled
- 0.6%
- Flights/day
- 7.2
- last 12 months
- Duration
- 2h 17m
- scheduled
- Distance
- 819 mi
Best airline from ONT to DEN
3 airlines flew this route regularly between 2024-07 and 2026-07.
| Airline | On-time | Avg delay | Cancelled | Flights |
|---|---|---|---|---|
| United Airlinesmost reliable | 84% | 13 min | 0.7% | 1,830 |
| Southwest Airlines | 79% | 13 min | 0.3% | 2,679 |
| Frontier Airlines | 79% | 17 min | 0.9% | 1,272 |
Monthly on-time trend
Best time to fly from ONT to DEN
Aim for departures around 5 a.m. (94% on-time); avoid 5 p.m. departures (58%).
By day of week
| Day | On-time | Avg delay |
|---|---|---|
| Monday | 79% | 14 min |
| Tuesday | 80% | 18 min |
| Wednesday | 79% | 15 min |
| Thursday | 80% | 15 min |
| Friday | 80% | 13 min |
| Saturdaybest | 85% | 10 min |
| Sunday | 82% | 13 min |
What causes delays on this route
Share of total delay minutes by cause, as reported by carriers to the US DOT.
- Late-arriving aircraft39%
- Airline operations20%
- National airspace system37%
- Weather4%
Frequently asked questions
- How often are flights from ONT to DEN delayed?
- 19% of ONT–DEN flights arrived 15 or more minutes late (the US DOT definition of a delay) between 2024-07 and 2026-07. The average arrival delay across completed flights was 14 minutes.
- Which airline is most reliable from ONT to DEN?
- United Airlines has the best on-time record on this route at 84%, based on 1,830 flights. 3 airlines flew ONT–DEN frequently enough to compare in this period.
- What is the best time of day to fly from ONT to DEN?
- Departures around 5 a.m. have the best record (94% on-time), while departures around 5 p.m. have the worst (58%). As on most US routes, delays accumulate through the day, so earlier flights are generally safer.
- How long is the flight from ONT to DEN?
- The scheduled ONT–DEN flight time averages 2h 17m over 819 miles. Actual arrival times vary — flights on this route land 15+ minutes late 19% of the time.
- How often are ONT to DEN flights cancelled?
- 0.6% of scheduled flights on this route were cancelled between 2024-07 and 2026-07, at or below the national rate of 1.6%.
- What is the worst month to fly from ONT to DEN?
- July 2025 was the roughest month in this dataset, with only 65% of arrivals on time. The best was September 2024 at 90%. If your dates are flexible, that 26-point gap is worth planning around.
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Based on 5,787 flights, 2024-07–2026-07. Source: US DOT Bureau of Transportation Statistics. Updated 2026-09-28.