Route reliability record
ATL→DEN
Atlanta to Denver
- Flights
- 5,589
- Period
- July 2025 to June 2026
- Distance
- 1,199 mi
- Carriers
- 4
This route lands a B, level with the national rate of 77.6%. Roughly 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 5,589 flights, of which United Airlines flew 967 at 85.6% on time.
United Airlines is the most reliable of the four carriers covered here at 85.6% on time across 967 flights.
Key figures
On time
77.6%
Arrivals under 15 minutes late, of 5,505 completed flights
Avg delay
60 min
Across delayed arrivals only, not all flights
Cancelled
1.02%
National rate is 1.81%
Best carrier
United
85.6% on time across 967 flights
These figures cover 5,589 flights between July 2025 and June 2026. The median arrival is 4 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 ATL to DEN
The choice of carrier is not cosmetic here. United Airlines arrives on time 85.6% of the time; Frontier Airlines manages 70.9%. Sample sizes sit next to every figure, because a two-point gap across 738 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 967 | 85.6% | 78 min | 0.41% | A+ |
| Delta Air Lines | 2,805 | 78.1% | 52 min | 1.11% | B |
| Southwest Airlines | 1,079 | 73.4% | 54 min | 1.11% | C |
| Frontier Airlines | 738 | 70.9% | 82 min | 1.36% | C |
The spread between United and Frontier is 15 points, wide enough that it should decide the booking. On a hundred trips that is 15 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 26 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am669 flights86.5%
- 8am–11am1,069 flights85.8%
- 11am–2pm1,017 flights86.1%
- 2pm–5pm1,132 flights75.3%
- 5pm–8pm812 flights60.4%
- 8pm–5am890 flights69.7%
Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 60.4% on time, against 86.5% 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 2pm–5pm window is the busiest, with 1,132 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 18 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.
December is the weak month at 68.2% on time, against 86.5% in November. 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. July was the busiest month here, with 526 flights.
Across the week, Wednesday is the strongest day at 83.5% on time and Sunday the weakest at 71.8%. 12 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 75,000 reported delay minutes.
- 34%Carrier
- 33%Late-arriving aircraft
- 28%National Airspace System
- 5%Extreme weather
- 0%Security
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 86.5% on time here. The split is drawn from 74,574 reported delay minutes.
No single cause dominates. carrier at 34%, late-arriving aircraft at 33% and national airspace system at 28% split the 75,000 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 1.02% against a national 1.81%, which is ordinary. Diversions add another 0.48%.
Connections and stage length
What a delay here actually costs
7.2% of arrivals land an hour or more late, close to the national 8.1%. 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 runs 80.0% on time across 5,596 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
The sample behind these figures is 5,589 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 December 68.2%, a swing of 18 points. If the dates move at all, move them out of December before you think about anything else. 5,505 completed flights over 12 months sit behind that.
Common questions
ATL to DEN questions
How often is ATL to DEN delayed?
Roughly 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 22.4% of the 5,589 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on ATL to DEN?
United Airlines leads at 85.6% on time across 967 flights. Frontier Airlines is at the other end on 70.9%, a gap of 15 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 5am–8am departure window is the strongest at 86.5% on time. The 5pm–8pm window is the weakest at 60.4%, 26 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 December delays on ATL to DEN?
December is the weakest month at 68.2% on time, compared with 86.5% in November. Across the year that is 18 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 record85.6%
- Delta Air Lines on-time record78.1%
- Southwest Airlines on-time record73.4%
- 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. 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, July 2025 to June 2026. Updated monthly. How this data is collected.