Ontario, CA · departure reliability
ONT
Ontario International
- Departures
- 25,791
- Period
- September 2025 to August 2026
- Carriers
- 7
- US rank
- #55 by volume
Ontario
Ontario International lands a B+, 5 points better than the national rate of 77.3%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 25,791 flights, of which Delta Air Lines flew 1,811 at 90.0% on time.
Delta Air Lines is the most reliable of the seven carriers covered here at 90.0% on time across 1,811 flights.
Key figures
On time
81.9%
Departures arriving under 15 minutes late at their destination
Avg delay
67 min
Across delayed flights only
Cancelled
0.87%
National rate is 1.89%
Best carrier
Delta
90.0% on time here
These figures cover 26,000 flights between September 2025 and August 2026. The median arrival is 7 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Carrier by carrier
Which airlines run best out of ONT
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 90.0% of the time; Frontier Airlines manages 75.2%. Sample sizes sit next to every figure, because a two-point gap across 2,284 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlines | 11,643 | 81.1% | 51 min | 0.42% | B+ |
| American Airlines | 3,545 | 83.3% | 103 min | 1.83% | B |
| United Airlines | 2,429 | 79.3% | 71 min | 0.54% | B+ |
| Frontier Airlines | 2,284 | 75.2% | 75 min | 1.31% | B |
| Alaska Airlines | 2,098 | 84.5% | 54 min | 1.29% | B |
| Delta Air Lines | 1,811 | 90.0% | 93 min | 1.49% | A |
| SkyWest Airlines | 1,771 | 87.4% | 78 min | 0.40% | A+ |
The spread between Delta and Frontier is 15 points, wide enough that it should decide the booking. On a hundred trips that is 15 more arrivals inside the on-time window.
Route by route
Busiest routes out of ONT
Route-level records vary far more than the airport average. These are the 15 busiest departures from ONT, each with its own on-time rate against the airport-wide 81.9%.
| Route | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| ONT to PHX · Phoenix | 3,011 | 82.4% | 72 min | 0.63% | B+ |
| ONT to DEN · Denver | 2,624 | 81.8% | 68 min | 0.38% | B+ |
| ONT to SEA · Seattle | 2,488 | 85.9% | 67 min | 1.13% | A |
| ONT to LAS · Las Vegas | 2,469 | 76.2% | 60 min | 0.93% | B+ |
| ONT to DFW · Dallas-Fort Worth | 2,274 | 80.8% | 96 min | 2.42% | B |
| ONT to SMF · Sacramento | 2,119 | 85.1% | 52 min | 0.28% | A+ |
| ONT to OAK · Oakland | 1,450 | 86.0% | 58 min | 0.55% | A+ |
| ONT to SFO · San Francisco | 1,335 | 60.7% | 63 min | 0.75% | D+ |
| ONT to SJC · San Jose | 1,320 | 85.9% | 57 min | 0.08% | A+ |
| ONT to SLC · Salt Lake City | 1,239 | 91.1% | 86 min | 0.89% | A+ |
| ONT to ATL · Atlanta | 934 | 89.0% | 100 min | 1.82% | A |
| ONT to IAH · Houston | 574 | 86.4% | 75 min | 1.22% | A |
| ONT to PDX · Portland | 565 | 91.4% | 64 min | 0.71% | A+ |
| ONT to HNL · Honolulu | 446 | 84.7% | 47 min | 0.22% | B+ |
| ONT to DAL · Dallas | 395 | 76.6% | 46 min | 1.52% | B |
Departure window
The best time of day to leave ONT
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 22 points, against 15 points between the best and worst carrier.
- 5am–8am6,824 flights93.1%
- 8am–11am4,054 flights85.2%
- 11am–2pm5,053 flights79.9%
- 2pm–5pm3,845 flights71.4%
- 5pm–8pm3,247 flights74.3%
- 8pm–5am2,768 flights77.0%
Scale runs 65% to 100%.
Book the early departure. Flights leaving between 5am–8am arrive on time 93.1% of the time, against 71.4% for the afternoon window. That is 22 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 6,824 flights scheduled in it.
Explore
Filter ONT departures by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On departures from Ontario (ONT), the best departure window is 5am–8am at 93.1% on time and the worst is 2pm–5pm at 71.4%, a wide gap of 21.7 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am93.1%
- 8–11am85.2%
- 11am–2pm79.9%
- 2–5pm71.4%
- 5–8pm74.3%
- 8pm–5am77.0%
best all US flightsScale 60% to 100%.
Across the year
When ONT runs late
Twelve months, one bar each, drawn from the same 25,791 flights. The strip shows how much of ONT's record is set by the calendar rather than by the operation.
June is the worst month at 76.7% on time, 11 points below February, the best at 87.8%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. July was the busiest month here, with 2,377 flights.
Across the week, Tuesday is the strongest day at 85.3% on time and Sunday the weakest at 80.0%, a spread of 5 points.
ONT month by month
Delay causes
Why ONT gets delayed
Late-arriving aircraft accounts for 42% of the 310,000 delay minutes carriers reported here, and the remaining four split what is left.
- 42%Late-arriving aircraft
- 34%Carrier
- 22%National Airspace System
- 1%Extreme weather
- 0%Security
42% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 310,000 reported delay minutes here, that single category outweighs weather by 30 to one. The split is drawn from 309,542 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 93.1% on time here.
Cancellations are rare at 0.87%, below the national 1.89% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
5.6% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.
25,791 flights sit behind these numbers, which is a large enough sample that the headline rate is not moving on noise. Where a sub-group falls below 30 flights the site shows a dash instead of a percentage.
What to do with this
Flying out of ONT
Put together: take the 5am–8am departure, avoid June if the dates are flexible, and if two carriers are within a few dollars of each other, Delta is the one with the record behind it. None of that guarantees an on-time arrival; it moves the odds by 22 points, which is the most any booking decision can do. 25,516 completed flights over 12 months sit behind that.
Common questions
ONT delay questions
How often is Ontario (ONT) delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 18.1% of the 25,791 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on Ontario (ONT)?
Delta Air Lines leads at 90.0% on time across 1,811 flights. Frontier Airlines is at the other end on 75.2%, a gap of 15 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on Ontario (ONT)?
The 5am–8am departure window is the strongest at 93.1% on time. The 2pm–5pm window is the weakest at 71.4%, 22 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are June delays on Ontario (ONT)?
June is the weakest month at 76.7% on time, compared with 87.8% in February. Across the year that is 11 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- ONT to PHX — Phoenix82.4%
- ONT to DEN — Denver81.8%
- ONT to SEA — Seattle85.9%
- ONT to LAS — Las Vegas76.2%
- ONT to DFW — Dallas-Fort Worth80.8%
- ONT to SMF — Sacramento85.1%
- Southwest Airlines on-time record81.1%
- American Airlines on-time record83.3%
- United Airlines on-time record79.3%
- Frontier Airlines on-time record75.2%
- Why the first flight of the morning is statistically safest
- US airports with the biggest gap between their best and worst month
Embed ONT’s on-time badge on your site
Paste this into a web page. The badge shows the current on-time rate, cancellation rate and grade, and updates every month. Preview it, or build a badge for another route or airport.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.