Route reliability record
ATL→ONT
Atlanta to Ontario
- Flights
- 934
- Period
- September 2025 to August 2026
- Distance
- 1,900 mi
- Carriers
- 1
This route sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.3%. The late ones land roughly 50 minutes behind schedule. That rests on 934 ATL to ONT flights, with a median arrival 2 minutes early.
Best time to fly ATL to ONT: a 8am–11am departure, ideally on a Wednesday. Flights in that window arrived on time 84.0% of the time and Wednesday flights 80.5%, against 74.2% for the route overall.
The US average over the same twelve months is 77.3%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
74.2%
Arrivals under 15 minutes late, of 917 completed flights
Avg delay
52 min
Across delayed arrivals only, not all flights
Cancelled
1.71%
National rate is 1.89%
Best carrier
Delta
74.2% on time across 934 flights
These figures cover 934 flights between September 2025 and August 2026. The median arrival is 2 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.
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Carrier by carrier
Which airline is most reliable on ATL 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 |
|---|---|---|---|---|---|
| Delta Air Lines | 934 | 74.2% | 52 min | 1.71% | C |
Flight by flight
Flights on ATL to ONT
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
Timetable by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Best ways to make this trip
The most reliable ways to fly Atlanta 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. 4 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. ATL → LAXAtlanta to Los Angeles | Delta Air Lines | 78.5% | 79.1% | 0.73% | 5am–8am, Wed | DL 898 08:05 |
| 2. ATL → SNAAtlanta to Santa Ana | Delta Air Lines | 75.3% | 76.0% | 0.88% | 2pm–5pm, Sat | DL 826 20:51 |
| 3. ATL → ONTAtlanta to Ontario | Delta Air Lines | 72.9% | 74.2% | 1.71% | 8am–11am, Wed | DL 665 09:41 |
| 4. ATL → LAXAtlanta to Los Angeles | American Airlines | 72.4% | 73.0% | 0.80% | 2pm–5pm, Wed | — |
| 5. ATL → LAXAtlanta to Los Angeles | Frontier Airlines | 69.4% | 70.5% | 1.63% | 8am–11am, Wed | F9 4315 10:35 |
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 16 points, against half a point between the best and worst carrier.
- 5am–8am—
- 8am–11am365 flights84.0%
- 11am–2pm—
- 2pm–5pm—
- 5pm–8pm385 flights68.0%
- 8pm–5am184 flights67.8%
Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 84.0% of the time, against 67.8% for the overnight window. That is 16 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 385 flights scheduled in it.
Explore
Filter ATL to ONT 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 ATL to ONT, the best departure window is 8am–11am at 84.0% on time and the worst is 8pm–5am at 67.8%, a wide gap of 16.2 points. All US flights leaving 8am–11am ran 83.9%.
- 5–8am—
- 8–11am84.0%
- 11am–2pm—
- 2–5pm—
- 5–8pm68.0%
- 8pm–5am67.8%
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 30 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.
July is the worst month at 58.6% on time, 30 points below March, the best at 88.3%. 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. May was the busiest month here, with 93 flights.
Across the week, Wednesday is the strongest day at 80.5% on time and Sunday the weakest at 70.6%, a spread of 10 points.
Delay causes
Why this route gets delayed
Carrier accounts for 44% of the 12,000 delay minutes carriers reported here, and the remaining four split what is left.
- 44%Carrier
- 28%Late-arriving aircraft
- 22%National Airspace System
- 5%Extreme weather
The largest share of delay minutes, 44%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 5,493 of the 12,000 delay minutes reported here. The split is drawn from 12,372 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 84.0% on time here.
Cancellations sit at 1.71% against a national 1.89%, which is ordinary. Diversions add another 0.11%.
Connections and stage length
What a delay here actually costs
7.7% 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 roughly 50 minutes, which a normal layover absorbs.
At 1,900 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.
The return leg is a different operation and performs like one: it runs 89.0% on time across 934 flights, 15 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 15 points of difference.
One caution: this is a thin sample. 934 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
Work out the risk of missing a connection in ONT after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 934 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 74.2% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 917 completed flights over 12 months sit behind that.
Common questions
ATL to ONT questions
How often is ATL to ONT delayed?
About one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 25.8% of the 934 flights in this analysis, against 22.7% nationally. Delayed flights are late by roughly 50 minutes on average.
How reliable is ATL to ONT compared with the rest of the country?
74.2% of flights arrive on time here against a national 77.3%, a difference of 3 points against it. That is worth a C on this site's grading scale.
What time of day has the fewest delays on ATL to ONT?
The 8am–11am departure window is the strongest at 84.0% on time. The 8pm–5am window is the weakest at 67.8%, 16 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 July delays on ATL to ONT?
July is the weakest month at 58.6% on time, compared with 88.3% in March. Across the year that is 30 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 ATL — the return legseparate record
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Ontario International (ONT) delay statistics
- ATL to LGA, a related route72.3%
- PHX to ONT, a related route76.8%
- ATL to MCO, a related route70.3%
- Delta Air Lines on-time record74.2%
- The best time of day to fly, according to 7.05 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. ATL to ONT and ONT to ATL 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.