Route reliability record
ONT→ATL
Ontario to Atlanta
- Flights
- 937
- Period
- July 2025 to June 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 13 points better than the national rate of 77.6%. When something does go wrong the average delay runs an hour and a half. That rests on 937 ONT to ATL flights, with a median arrival 12 minutes early.
Best time to fly ONT to ATL: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 93.8% of the time and Wednesday flights 93.9%, against 90.3% for the route overall.
Set against the rest of the country, this route's record is 13 points better than the US average of 77.6%. That gap is worth roughly 127 fewer late arrivals for every thousand flights.
Key figures
On time
90.3%
Arrivals under 15 minutes late, of 913 completed flights
Avg delay
99 min
Across delayed arrivals only, not all flights
Cancelled
1.81%
National rate is 1.81%
Best carrier
Delta
90.3% on time across 937 flights
These figures cover 937 flights between July 2025 and June 2026. The median arrival is 12 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 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 | 937 | 90.3% | 99 min | 1.81% | 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.
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 | 88.7% | 90.3% | 1.81% | 5am–8am, Wed | DL 761 07:05 |
| 2. LAX → ATLLos Angeles to Atlanta | Delta Air Lines | 80.8% | 81.5% | 0.86% | 5am–8am, Wed | DL 390 06:00 |
| 3. SNA → ATLSanta Ana to Atlanta | Delta Air Lines | 80.2% | 81.1% | 1.05% | 8pm–5am, Mon | DL 721 06:45 |
| 4. LAX → ATLLos Angeles to Atlanta | American Airlines | 66.4% | 66.8% | 0.53% | 8am–11am, Wed | — |
| 5. LAX → ATLLos Angeles to Atlanta | Frontier Airlines | 59.1% | 60.1% | 1.73% | 2pm–5pm, Tue | F9 4316 15:28 |
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 937 flights.
- 5am–8am266 flights93.8%
- 8am–11am—
- 11am–2pm365 flights85.9%
- 2pm–5pm—
- 5pm–8pm—
- 8pm–5am306 flights92.3%
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 85.9% on time against 93.8% for 5am–8am. 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.
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, Wednesday is the strongest day at 93.9% on time and Saturday the weakest at 87.5%. 6 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. Carrier accounts for 63% of the 8,836 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.
- 63%Carrier
- 28%Late-arriving aircraft
- 6%National Airspace System
- 2%Security
The largest share of delay minutes, 63%, 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 5,596 of the 8,836 delay minutes reported here. The split is drawn from 8,836 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 93.8% on time here.
Cancellations sit at 1.81% against a national 1.81%, which is ordinary. Diversions add another 0.75%.
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 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 76.6% on time across 937 flights, 14 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 14 points of difference.
One caution: this is a thin sample. 937 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. 937 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 90.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 913 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 ten arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 9.7% of the 937 flights in this analysis, against 22.4% nationally. Delayed flights are late by an hour and a half on average.
How reliable is ONT to ATL compared with the rest of the country?
90.3% of flights arrive on time here against a national 77.6%, a difference of 13 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 5am–8am departure window is the strongest at 93.8% on time. The 11am–2pm window is the weakest at 85.9%, 8 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
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- ONT to PHX, a related route82.7%
- LGA to ATL, a related route76.6%
- ONT to DEN, a related route79.7%
- Delta Air Lines on-time record90.3%
- Worst months to fly in the US, ranked by the data
- How to read this site: grades, sample sizes, and honest caveats
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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.