Route reliability record
ONT→ATL
Ontario to Atlanta
- Flights
- 934
- Period
- September 2025 to August 2026
- Distance
- 1,900 mi
- Carriers
- 1
This route earns an A. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 12 points better than the national rate of 77.3%. When something does go wrong the average delay runs close to two hours. That rests on 934 ONT to ATL flights, with a median arrival 10 minutes early.
Best time to fly ONT to ATL: a 8pm–5am departure, ideally on a Tuesday. Flights in that window arrived on time 92.6% of the time and Tuesday flights 93.0%, against 89.0% for the route overall.
Set against the rest of the country, this route's record is 12 points better than the US average of 77.3%. That gap is worth roughly 117 fewer late arrivals for every thousand flights.
Key figures
On time
89.0%
Arrivals under 15 minutes late, of 907 completed flights
Avg delay
100 min
Across delayed arrivals only, not all flights
Cancelled
1.82%
National rate is 1.89%
Best carrier
Delta
89.0% on time across 934 flights
These figures cover 934 flights between September 2025 and August 2026. The median arrival is 10 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 ONT to ATL
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 | 89.0% | 100 min | 1.82% | A |
Flight by flight
Flights on ONT to ATL
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.
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Best ways to make this trip
The most reliable ways to fly Ontario to Atlanta
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. ONT → ATLOntario to Atlanta | Delta Air Lines | 87.4% | 89.0% | 1.82% | 8pm–5am, Tue | DL 761 07:05 |
| 2. LAX → ATLLos Angeles to Atlanta | Delta Air Lines | 80.1% | 80.8% | 0.84% | 5am–8am, Wed | DL 390 06:00 |
| 3. SNA → ATLSanta Ana to Atlanta | Delta Air Lines | 79.1% | 79.9% | 0.98% | 8pm–5am, Thu | DL 721 06:45 |
| 4. LAX → ATLLos Angeles to Atlanta | Frontier Airlines | 67.1% | 68.2% | 1.64% | 2pm–5pm, Thu | F9 3216 23:34 |
| 5. LAX → ATLLos Angeles to Atlanta | American Airlines | 66.1% | 66.5% | 0.53% | 8am–11am, Thu | — |
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 is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 934 flights.
- 5am–8am266 flights91.9%
- 8am–11am—
- 11am–2pm365 flights83.9%
- 2pm–5pm—
- 5pm–8pm—
- 8pm–5am303 flights92.6%
Scale runs 75% to 100%. Rows with fewer than 30 flights show a dash.
The weak window here is the middle of the day, not the evening: 11am–2pm runs 83.9% on time against 92.6% for 8pm–5am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 11am–2pm window is the busiest, with 365 flights scheduled in it.
Explore
Filter ONT to ATL 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 ONT to ATL, the best departure window is 8pm–5am at 92.6% on time and the worst is 11am–2pm at 83.9%, a real gap of 8.7 points. All US flights leaving 8pm–5am ran 70.1%.
- 5–8am91.9%
- 8–11am—
- 11am–2pm83.9%
- 2–5pm—
- 5–8pm—
- 8pm–5am92.6%
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 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.
January is the weak month at 77.0% on time, against 97.4% in September. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. May was the busiest month here, with 93 flights.
Across the week, Tuesday is the strongest day at 93.0% on time and Saturday the weakest at 85.5%, a spread of 8 points.
Delay causes
Why this route gets delayed
Carrier accounts for 69% of the 10,000 delay minutes carriers reported here, and the remaining four split what is left.
- 69%Carrier
- 22%Late-arriving aircraft
- 8%National Airspace System
- 2%Security
The largest share of delay minutes, 69%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 6,918 of the 10,000 delay minutes reported here. The split is drawn from 10,028 reported delay minutes.
Cancellations sit at 1.82% against a national 1.89%, which is ordinary. Diversions add another 1.07%.
Connections and stage length
What a delay here actually costs
5.1% 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 close to two hours, 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 74.2% on time across 934 flights, 15 points below 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 ATL 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 89.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 907 completed flights over 12 months sit behind that.
Common questions
ONT to ATL questions
How often is ONT to ATL delayed?
About one flight in nine arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 11.0% of the 934 flights in this analysis, against 22.7% nationally. Delayed flights are late by close to two hours on average.
How reliable is ONT to ATL compared with the rest of the country?
89.0% of flights arrive on time here against a national 77.3%, a difference of 12 points in its favour. That is worth a A on this site's grading scale.
What time of day has the fewest delays on ONT to ATL?
The 8pm–5am departure window is the strongest at 92.6% on time. The 11am–2pm window is the weakest at 83.9%, 9 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 January delays on ONT to ATL?
January is the weakest month at 77.0% on time, compared with 97.4% in September. 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
- ATL to ONT — the return legseparate record
- Ontario International (ONT) delay statistics
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- ONT to PHX, a related route82.4%
- LGA to ATL, a related route75.5%
- ONT to DEN, a related route81.8%
- Delta Air Lines on-time record89.0%
- The most punctual routes in the US, and the least
- The best time of day to fly, according to 7.05 million flight records
Direction matters. ONT to ATL and ATL to ONT 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.