Route reliability record
OAK→ONT
Oakland to Ontario
- Flights
- 1,489
- Period
- July 2025 to June 2026
- Distance
- 362 mi
- Carriers
- 1
This route lands a B+, 5 points better than the national rate of 77.6%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about 50 minutes on average. That is a workable record, not a spotless one. That rests on 1,489 OAK to ONT flights, with a median arrival 7 minutes early.
Best time to fly OAK to ONT: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 97.5% of the time and Wednesday flights 86.6%, against 82.5% for the route overall.
Set against the rest of the country, this route's record is 5 points better than the US average of 77.6%. That gap is worth roughly 49 fewer late arrivals for every thousand flights.
Key figures
On time
82.5%
Arrivals under 15 minutes late, of 1,482 completed flights
Avg delay
49 min
Across delayed arrivals only, not all flights
Cancelled
0.40%
National rate is 1.81%
Best carrier
Southwest
82.5% on time across 1,489 flights
These figures cover 1,489 flights between July 2025 and June 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 airline is most reliable on OAK to ONT
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlines | 1,489 | 82.5% | 49 min | 0.40% | B+ |
Best ways to make this trip
The most reliable ways to fly Oakland to Ontario
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 5 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SJC → LAXSan Jose to Los Angeles | SkyWest Airlines | 92.2% | 92.6% | 0.39% | 5am–8am, Thu | OO 3979 07:00 |
| 2. SJC → LAXSan Jose to Los Angeles | Delta Air Lines | 89.5% | 92.3% | 3.08% | 11am–2pm, Sun | — |
| 3. SJC → SNASan Jose to Santa Ana | Southwest Airlines | 86.3% | 87.0% | 0.83% | 5am–8am, Sat (route) | — |
| 4. OAK → LGBOakland to Long Beach | Southwest Airlines | 86.1% | 86.3% | 0.25% | 5am–8am, Tue | — |
| 5. SJC → LGBSan Jose to Long Beach | Southwest Airlines | 85.4% | 85.5% | 0.16% | 5am–8am, Wed | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 36 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am327 flights97.5%
- 8am–11am212 flights92.0%
- 11am–2pm297 flights83.8%
- 2pm–5pm201 flights75.1%
- 5pm–8pm231 flights77.7%
- 8pm–5am221 flights61.5%
Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 61.5% on time, against 97.5% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 327 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 20 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
June is the worst month at 74.1% on time, 20 points below January, the best at 94.1%. 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. October was the busiest month here, with 136 flights.
Across the week, Wednesday is the strongest day at 86.6% on time and Thursday the weakest at 76.8%. 10 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Late-arriving aircraft accounts for 58% of the 13,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 58%Late-arriving aircraft
- 38%Carrier
- 4%National Airspace System
58% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 13,000 reported delay minutes here, that single category outweighs weather by 58 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 12,733 reported delay minutes.
The largest share of delay minutes, 38%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 4,888 of the 13,000 delay minutes reported here.
Cancellations are rare at 0.40%, below the national 1.81% 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.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.3% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
At 362 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 5am–8am window matters as much as it does.
The return leg is a different operation and performs like one: it runs 86.3% on time across 1,490 flights, 4 points above this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 4 points of difference.
The sample behind these figures is 1,489 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in ONT after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 94.1% on time and June 74.1%, a swing of 20 points. If the dates move at all, move them out of June before you think about anything else. 1,482 completed flights over 12 months sit behind that.
Common questions
OAK to ONT questions
How often is OAK to 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 17.5% of the 1,489 flights in this analysis, against 22.4% nationally. Delayed flights are late by about 50 minutes on average.
How reliable is OAK to ONT compared with the rest of the country?
82.5% of flights arrive on time here against a national 77.6%, a difference of 5 points in its favour. That is worth a B+ on this site's grading scale.
What time of day has the fewest delays on OAK to ONT?
The 5am–8am departure window is the strongest at 97.5% on time. The 8pm–5am window is the weakest at 61.5%, 36 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 OAK to ONT?
June is the weakest month at 74.1% on time, compared with 94.1% in January. Across the year that is 20 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 OAK — the return legseparate record
- Oakland International (OAK) delay statistics
- OAK to LAS, a related route78.1%
- PHX to ONT, a related route77.7%
- OAK to SAN, a related route66.9%
- Southwest Airlines on-time record82.5%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
Direction matters. OAK to ONT and ONT to OAK are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.