81% of flights leaving Ontario (ONT) arrived on time over the past 12 months, 6 points better than the national average of 76%. That ranks 9 of 76 large U.S. airports. About 73 flights leave ONT on a typical day; 0.9% were cancelled. 80% pushed back from the gate on time, so most of the lateness is already there when the flight leaves the gate.
At a glance
- Best hour to fly: 5 a.m. (95% on time). Worst: 8 p.m. (68%).
- Best month: February (87%). Worst: July (78%).
- Most reliable airline here: Delta Air Lines (89%), vs Frontier Airlines at 74%.
- Biggest delay cause: late-arriving aircraft (42% of delay minutes).
- Year on year: getting worse (84% → 81%).
How late?
The on-time rate treats a flight 20 minutes late the same as one 5 hours late. Here's the split for flights leaving ONT: when a flight was late, it was under 45 minutes late 59% of the time. About 1 in 19 flights landed an hour or more late, and 1 in 96 three hours or more; 0.9% were cancelled outright.
- On time or early81%
- 15–30 min late7.1%
- 30–60 min late5.2%
- 1–2 hours late3.3%
- 2–3 hours late1.0%
- 3+ hours late1.0%
- Diverted0.2%
- Cancelled0.9%
Share of all 26,554 scheduled flights, past 12 months, by arrival time against schedule.
Best time of day to fly out of ONT
Time of day matters more at ONT than almost anything else you control. Flights scheduled to leave at 5 a.m. arrived on time 95% of the time; at 8 p.m. it was 68%, a 27-point gap. Taken together, early departures (5–9 a.m.) ran 91% on time against 73% for the evening bank (5–10 p.m.). Early planes usually start the day at the airport, so they haven't had a chance to pick up delays elsewhere. By evening a late inbound aircraft, a crew running out of duty hours or an afternoon thunderstorm can push one late flight into the next. Cancellations cluster too: 11 p.m. departures were cancelled 2.9% of the time, against 0.9% overall.
Hour × month
Combine the two and the spread is wider still. The most reliable combination at ONT was a 5 a.m. departure in April (98% on time); the least, 8 p.m. in June (59%). If you can only move one thing, move the hour. Departure hour usually shifts the odds more than the month does.
Each cell: on-time rate for that departure hour in that calendar month, 2023–2026. Find your travel month, then look along the row for the greenest hour.
Best and worst months
July is the hardest month at ONT, with 78% of flights on time across 2023–2026; February is the best at 87%. Summer (June–August) runs 6 points worse than autumn: heavy schedules, peak loads and afternoon thunderstorms. Cancellations peak in January (1.9% of flights).
Airlines at ONT
Southwest Airlines runs 44% of departures from ONT. Among airlines with at least 1,000 departures here, Delta Air Lines was the most reliable (89% on time) and Frontier Airlines the least (74%), a 15-point difference. On a route where both fly, that difference is worth more than a small fare gap.
| Airline | Departures | On time | Left on time | Cancelled | Typical arrival |
|---|---|---|---|---|---|
| Southwest Airlines | 11,643 | 81% | 77% | 0.4% | −6 min |
| American Airlines | 3,636 | 81% | 82% | 1.8% | −10 min |
| Delta Air Lines | 3,205 | 89% | 89% | 1.0% | −12 min |
| Alaska Airlines | 3,053 | 85% | 85% | 1.2% | −8 min |
| United Airlines | 2,568 | 77% | 81% | 0.6% | −5 min |
| Frontier Airlines | 2,284 | 74% | 76% | 1.3% | −7 min |
| JetBlue | 165 | 61% | 55% | 4.2% | −4 min |
Why flights are late at ONT
Airlines report a cause for every flight that arrives 15 or more minutes late. At ONT, 42% of delay minutes came from late-arriving aircraft: the plane showed up late from its previous flight, so the delay started somewhere else. Next is the airlines themselves at 34%. That's why the first flight of the morning is the safest bet: it has no earlier flight to inherit a delay from. Of the 235 cancellations, 37% were blamed on weather, so most were within the airlines’ control or the air traffic system’s.
The average taxi from gate to takeoff is 14 minutes, shorter than at most large U.S. airports.
ONT vs nearby airports
ONT isn't the only option in Los Angeles. Over the past year LAX ran 78% on time with 1.0% of flights cancelled; BUR ran 80% on time with 1.3% of flights cancelled; LGB ran 84% on time with 0.4% of flights cancelled; SNA ran 80% on time with 1.1% of flights cancelled, against 81% and 0.9% at ONT. LGB has the better record, so if fares and times are close, it is the safer pick.
| Airport | Distance | Departures | On time | Cancelled |
|---|---|---|---|---|
| ONT Ontario | — | 26,554 | 81% | 0.9% |
| SNA Orange County John Wayne | 30 mi | 45,942 | 80% | 1.1% |
| LGB Long Beach | 36 mi | 14,934 | 84% | 0.4% |
| BUR Hollywood Burbank | 44 mi | 30,220 | 80% | 1.3% |
| LAX Los Angeles LAX | 47 mi | 193,950 | 78% | 1.0% |
Month by month
Over the latest 12 months 81% of ONT departures were on time, against 84% in the 12 months before, a decline of 3 points. The best recent month was February 2026 (88%); the worst, June 2026 (76%).
Worst cancellation days
The worst single day in the past year was Saturday, Jan 24, 2026, when 12% of 51 scheduled departures were cancelled. Days like that are usually a major storm, a system outage or a holiday peak hitting bad weather. No average predicts them, so on a stormy forecast, check your airline's travel waivers.
| Date | Departures | Cancelled | On time |
|---|---|---|---|
| Jan 24, 2026 | 51 | 12% | 82% |
| Jan 25, 2026 | 68 | 9% | 75% |
| Nov 10, 2025 | 81 | 9% | 54% |
| Nov 9, 2025 | 83 | 8% | 65% |
| Jan 26, 2026 | 64 | 8% | 75% |
| Nov 13, 2025 | 82 | 6% | 82% |
| Nov 11, 2025 | 67 | 6% | 90% |
| Nov 20, 2025 | 74 | 5% | 82% |
| May 19, 2026 | 76 | 5% | 62% |
| Jan 27, 2026 | 57 | 5% | 81% |
Last flights of the day
The last flight of the day is a different bet. Across routes from ONT, each airline's final departure was cancelled 0.9% of the time, against 0.9% for its earlier flights, about the same. 1.4% of last flights landed 3+ hours late. The riskiest last flight out was Frontier Airlines to Las Vegas (1.4% cancelled).
| Last flight to | Airline | Leaves | Cancelled | 3h+ late | On time |
|---|---|---|---|---|---|
| LAS Las Vegas | Frontier Airlines | 3:40 p.m. | 1.4% | 2.7% | 69% |
| DFW Dallas | American Airlines | 11:59 p.m. | 3.0% | 0.5% | 79% |
| SFO San Francisco | United Airlines | 6:39 p.m. | 0.8% | 2.8% | 48% |
| DEN Denver | United Airlines | 1:18 p.m. | 0.5% | 2.8% | 79% |
| ATL Atlanta | Delta Air Lines | 10:00 p.m. | 1.9% | 1.4% | 90% |
| DEN Denver | Southwest Airlines | 2:30 p.m. | 0.3% | 2.2% | 59% |
| SLC Salt Lake City | Delta Air Lines | 5:10 p.m. | 0.8% | 1.6% | 89% |
| OAK Oakland | Southwest Airlines | 7:35 p.m. | 1.1% | 1.4% | 77% |
| PHX Phoenix | American Airlines | 7:13 p.m. | 1.1% | 1.1% | 76% |
| SEA Seattle | Alaska Airlines | 7:59 p.m. | 0.5% | 1.6% | 73% |
| DEN Denver | Frontier Airlines | 10:49 a.m. | 0.5% | 1.5% | 83% |
| SEA Seattle | Delta Air Lines | 6:01 p.m. | 0.3% | 1.1% | 88% |
Each airline's last scheduled departure of the day on a route, on days it flies the route at least twice; past 12 months. Riskiest first.
Tips for flying out of ONT
- Book the earliest departure you can live with. At ONT the 5 a.m. flights do best.
- Traveling in July? Leave extra slack for anything that can't move: cruises, weddings, the last connection of the day.
- Choosing between airlines? Delta Air Lines has the better record here.
- Delayed already? Most delays at ONT come from late-arriving aircraft. If your inbound plane is late, your flight will be too, whatever the board says.
Routes from ONT
Where you're going matters too. From ONT, the most reliable busy route was to Salt Lake City (SLC, 90% on time) and the least reliable to San Francisco (SFO, 60%). Flights into congested airports inherit their delays: an air traffic program at the destination holds planes on the ground here.
Least reliable first. Routes with at least 365 flights a year.
| To | Flights | On time | Cancelled | Typical arrival |
|---|---|---|---|---|
| SFO San Francisco | 1,335 | 60% | 0.8% | +4 min |
| DAL Dallas | 395 | 75% | 1.5% | +4 min |
| LAS Las Vegas | 2,469 | 76% | 0.9% | −5 min |
| DFW Dallas | 2,274 | 78% | 2.4% | −9 min |
| DEN Denver | 2,624 | 81% | 0.4% | −6 min |
| PHX Phoenix | 3,011 | 82% | 0.6% | −6 min |
| HNL Honolulu | 446 | 85% | 0.2% | −7 min |
| SMF Sacramento | 2,119 | 85% | 0.3% | −10 min |
| SEA Seattle | 2,488 | 85% | 1.1% | −9 min |
| IAH Houston | 574 | 85% | 1.2% | −6 min |
| OAK Oakland | 1,450 | 86% | 0.5% | −11 min |
| SJC San Jose | 1,320 | 86% | 0.1% | −10 min |
| ATL Atlanta | 934 | 86% | 1.8% | −10 min |
| SLC Salt Lake City | 1,239 | 90% | 0.9% | −14 min |
| PDX Portland | 1,065 | 90% | 1.1% | −11 min |
Flights into ONT
Arriving rather than leaving? These are the routes into Ontario, least reliable first. The weakest is from Dallas (67% on time).
| From | Flights | On time | Cancelled |
|---|---|---|---|
| DAL Dallas | 395 | 67% | 1.3% |
| DFW Dallas | 2,274 | 70% | 2.2% |
| ATL Atlanta | 934 | 73% | 1.7% |
| HNL Honolulu | 446 | 74% | 0.2% |
| DEN Denver | 2,623 | 75% | 0.2% |
| LAS Las Vegas | 2,473 | 75% | 0.7% |
| SFO San Francisco | 1,337 | 76% | 0.8% |
| PHX Phoenix | 3,012 | 76% | 0.5% |
| OAK Oakland | 1,458 | 80% | 0.5% |
| IAH Houston | 574 | 81% | 0.2% |
| SEA Seattle | 2,487 | 82% | 1.1% |
| SJC San Jose | 1,318 | 82% | 0.1% |
| SMF Sacramento | 2,108 | 84% | 0.3% |
| PDX Portland | 1,066 | 85% | 0.9% |
| SLC Salt Lake City | 1,239 | 88% | 0.9% |
Questions about ONT delays
What is the best time to fly out of ONT?
Flights scheduled at 5 a.m.: over the past year 95% of ONT departures at that hour arrived on time, against 68% at 8 p.m., the worst hour.
What month has the most flight delays at ONT?
July (78% on time). February is the best month (87%).
Which airline is most on time at ONT?
Delta Air Lines: 89% of its ONT departures arrived on time over the past year. Frontier Airlines had the weakest record at 74%.
Why are flights delayed at ONT?
The biggest cause was late-arriving aircraft (42% of delay minutes): the plane showed up late from its previous flight, so the delay started somewhere else. Then the airlines themselves (34%).
Is ONT or LAX or BUR or LGB or SNA more reliable?
Over the past year: ONT 81% on time, LAX 78%, BUR 80%, LGB 84%, SNA 80%.
How often are flights cancelled at ONT?
0.9% of scheduled departures over the past 12 months, peaking in January at 1.9%.
Hours are scheduled local departure times. "On time" means arriving less than 15 minutes late at the destination; cancelled and diverted flights count as not on time. Method.