Ontario (ONT) Flight Delays: Rate, Best Hours and Airlines
Ontario (ONT) is covered here with a statistics page (it is not one of the 22 full guide airports): 16.6% of flights departing ONT arrived 15 or more minutes late across 75,772 flights, January 2023 to December 2025. Southwest Airlines operated 44.7% of those departures, with a 15.7% delay rate of its own. The worst scheduled departure hours are 9 PM (28.9%) and 3 PM (27.0%); 5 AM is the best at 4.9%. 0.90% of scheduled ONT departures were cancelled in 2024 to 2025.
Delay window: January 2023 to December 2025. Cancellation window: 2024 to 2025. Last updated: 2026-10-01. Delayed means a flight arrived 15 or more minutes after its scheduled arrival, the BTS and DOT on-time standard. Cancelled and diverted flights are excluded from delay rates. Historical BTS figures are separate from DelayGuard's per-flight model probability and from live FAA, weather and ground-delay status.
Predict a ONT flight
Historical BTS on-time (15+ min) at ONT
Sample size: 75,772 flights, window: January 2023 to December 2025. Delay rate 16.6%. Cancellation rate 0.90% of 52,337 scheduled flights, 2024 to 2025.
Why ONT runs the way it does
Southwest Airlines flew 44.7% of ONT departures in the window, and its flights ran 15.7% late against 16.6% for the airport as a whole. With one carrier that large, ONT's delay record largely follows how Southwest Airlines runs its schedule.
ONT delays peak in June (20.5%), July (20.1%) and May (18.5%) and are lowest in November (14.1%). That shape is consistent with the summer thunderstorm season, when convective weather builds through the afternoon and slows arrivals and departures.
Delays build through the day: 7.9% of flights scheduled before 8 AM ran late against 22.7% after 8 PM. That is the pattern BTS describes as late-arriving aircraft, where a previous flight with the same aircraft arriving late makes the next departure late.
Best and worst times to fly from ONT
ONT delay rate by scheduled departure hour (hours with 100+ flights)| Hour | Delayed 15+ min | Flights |
|---|
| 12 AM | 20.4% | 594 |
| 5 AM | 4.9% | 4,846 |
| 6 AM | 7.6% | 10,222 |
| 7 AM | 10.3% | 4,329 |
| 8 AM | 12.7% | 4,256 |
| 9 AM | 9.8% | 3,179 |
| 10 AM | 15.5% | 5,521 |
| 11 AM | 15.2% | 3,987 |
| 12 PM | 17.4% | 5,010 |
| 1 PM | 19.4% | 5,122 |
| 2 PM | 25.3% | 3,374 |
| 3 PM | 27.0% | 2,796 |
| 4 PM | 24.1% | 4,053 |
| 5 PM | 22.0% | 3,712 |
| 6 PM | 24.3% | 3,512 |
| 7 PM | 22.9% | 3,388 |
| 8 PM | 23.1% | 2,628 |
| 9 PM | 28.9% | 1,425 |
| 10 PM | 17.1% | 2,194 |
| 11 PM | 24.2% | 1,624 |
ONT delays and cancellations by month
ONT by month| Month | Delayed 15+ min | Flights | Cancelled |
|---|
| Jan | 15.8% | 5,551 | 2.09% |
| Feb | 14.6% | 5,170 | 0.74% |
| Mar | 18.0% | 6,053 | 0.46% |
| Apr | 16.5% | 6,229 | 0.46% |
| May | 18.5% | 6,567 | 0.87% |
| Jun | 20.5% | 6,514 | 1.04% |
| Jul | 20.1% | 6,816 | 1.69% |
| Aug | 17.3% | 6,793 | 0.85% |
| Sep | 14.2% | 6,532 | 0.40% |
| Oct | 14.4% | 6,833 | 0.37% |
| Nov | 14.1% | 6,419 | 1.36% |
| Dec | 14.6% | 6,295 | 0.52% |
Airlines at ONT
Regional operators are reported separately from the airline brands they fly for.
Routes from ONT
Routes from ONT (500+ flights)| Route | Delayed 15+ min | Flights | Cancelled | Link |
|---|
| ONT to PHX | 15.4% | 9,236 | 0.52% | Predict |
| ONT to DEN | 17.6% | 8,339 | 0.68% | Predict |
| ONT to LAS | 22.5% | 7,936 | 0.88% | Predict |
| ONT to SEA | 13.8% | 7,349 | 1.17% | Predict |
| ONT to DFW | 20.7% | 6,923 | 2.27% | Predict |
| ONT to SMF | 13.1% | 5,849 | 0.25% | Predict |
| ONT to OAK | 13.9% | 4,734 | 0.48% | Predict |
| ONT to SJC | 13.2% | 4,217 | 0.19% | Predict |
| ONT to SFO | 25.2% | 4,197 | 1.23% | Predict |
| ONT to SLC | 8.6% | 3,496 | 0.86% | Predict |
| ONT to ATL | 9.5% | 2,865 | 1.30% | Predict |
| ONT to PDX | 13.6% | 1,614 | 1.71% | Predict |
| ONT to DAL | 15.5% | 1,119 | 0.90% | Predict |
| ONT to HNL | 20.8% | 1,089 | 0.54% | Predict |
| ONT to AUS | 13.7% | 1,072 | 0.28% | Predict |
Los Angeles (LAX) full delay guide
Questions
- How often are flights delayed at ONT?
- 16.6% of flights departing ONT arrived 15 or more minutes late across 75,772 flights, January 2023 to December 2025 (BTS). Across all US domestic flights in the data, the rate is 21.2%.
- What is the best time to fly from ONT?
- Early departures run best. 5 AM flights ran 4.9% late (4,846 flights), 6 AM flights ran 7.6% late (10,222 flights) and 9 AM flights ran 9.8% late (3,179 flights). The worst hours are 9 PM (28.9%), 3 PM (27.0%) and 2 PM (25.3%).
- Which month is worst for delays at ONT?
- June has the highest delay rate at 20.5%. November is the lowest at 14.1%.
- Which airline has the best on-time record at ONT?
- Among carriers still flying with at least 5,000 flights from ONT, Delta Air Lines has the lowest delay rate at 9.4% (5,981 flights). Frontier Airlines is highest at 25.7%. Regional operators such as SkyWest are reported separately from the airline brands they fly for.
- How often are ONT flights cancelled?
- 0.90% of 52,337 scheduled departures from ONT were cancelled in 2024 to 2025. The US figure over the same period is 1.41%. See the full ranking on the cancellation rates page.
- Does DelayGuard show live delays at ONT?
- The predictor covers ONT flights with a model probability that combines history, weather and FAA data. This page shows historical BTS figures only.
- Is ONT better than nearby airports?
- Compare ONT with LAX (18.4%), BUR (17.6%) and SNA (18.2%) on the Los Angeles area: LAX vs BUR vs SNA vs ONT compared page. Those are the delay rates for flights departing each airport over the same window.