Route reliability record
ATL→DEN
Atlanta to Denver
- Flights
- 5,582
- Period
- June 2025 to May 2026
- Distance
- 1,199 mi
- Carriers
- 4
This route lands a B, about a point worse than the national rate of 77.4%. About one flight in four arrive 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 5,582 flights, of which United Airlines flew 992 at 84.9% on time.
United Airlines is the most reliable of the four carriers covered here at 84.9% on time across 992 flights.
Key figures
On time
76.0%
Arrivals under 15 minutes late, of 5,497 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
1.09%
National rate is 1.80%
Best carrier
United
84.9% on time across 992 flights
These figures cover 5,582 flights between June 2025 and May 2026. Beyond the headline rate, 8.1% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Carrier by carrier
Which airline is most reliable on ATL to DEN
The choice of carrier is not cosmetic here. United Airlines arrives on time 84.9% of the time; Frontier Airlines manages 68.4%. Sample sizes sit next to every figure, because a two-point gap across 704 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 992 | 84.9% | 77 min | 0.40% | B+ |
| Delta Air Lines | 2,803 | 76.2% | 54 min | 1.21% | B |
| Southwest Airlines | 1,083 | 72.5% | 59 min | 1.29% | C |
| Frontier Airlines | 704 | 68.4% | 77 min | 1.28% | C |
The spread between United and Frontier is 17 points, wide enough that it should decide the booking. On a hundred trips that is 17 more arrivals inside the on-time window.
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 30 points, against 17 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am665 flights85.0%
- 8am–11am1,057 flights85.6%
- 11am–2pm1,027 flights85.3%
- 2pm–5pm1,119 flights74.9%
- 5pm–8pm827 flights55.8%
- 8pm–5am887 flights67.4%
Scale runs 45% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 55.8% on time, against 85.6% for the 8am–11am 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.
Across the year
When delays peak on this route
This route's year swings by 26 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 60.7% on time, 26 points below November, the best at 86.5%. 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.
Across the week, Wednesday is the strongest day at 82.1% on time and Sunday the weakest at 71.2%. 11 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 81,000 reported delay minutes.
- 34%Carrier
- 31%Late-arriving aircraft
- 29%National Airspace System
- 6%Extreme weather
- 0%Security
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 85.6% on time here.
No single cause dominates. carrier at 34%, late-arriving aircraft at 31% and national airspace system at 29% split the 81,000 reported delay minutes between them. An even spread like this usually means the operation is running close to its designed capacity with no one obvious weak point, and it is the hardest pattern for a traveller to route around.
Cancellations sit at 1.09% against a national 1.80%, which is ordinary. Diversions add another 0.43%.
Connections and stage length
What a delay here actually costs
8.1% of arrivals land an hour or more late, close to the national 8.2%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route are the about an hour kind, which a normal layover absorbs.
The 1,199 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg is a different operation and performs like one: it runs 79.6% on time across 5,586 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 5,582 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.
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. November runs 86.5% on time and June 60.7%, a swing of 26 points. If the dates move at all, move them out of June before you think about anything else.
Common questions
ATL to DEN questions
How often is ATL to DEN delayed?
About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 24.0% of the 5,582 flights in this analysis, against 22.6% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on ATL to DEN?
United Airlines leads at 84.9% on time across 992 flights. Frontier Airlines is at the other end on 68.4%, a gap of 17 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 ATL to DEN?
The 8am–11am departure window is the strongest at 85.6% on time. The 5pm–8pm window is the weakest at 55.8%, 30 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 ATL to DEN?
June is the weakest month at 60.7% on time, compared with 86.5% in November. Across the year that is 26 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
- DEN to ATL — the return legseparate record
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Denver International (DEN) delay statistics
- United Airlines on-time record84.9%
- Delta Air Lines on-time record76.2%
- Southwest Airlines on-time record72.5%
- 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 DEN and DEN to ATL are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, June 2025 to May 2026. Updated monthly. How this data is collected.