Carrier route record
WNATL→DEN
Southwest Airlines · Atlanta to Denver
- Flights
- 1,079
- Period
- July 2025 to June 2026
- Share of route
- 19%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on ATL to DEN sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 4 points worse than the national rate of 77.6%. The late ones land about 55 minutes behind schedule. That rests on 1,079 flights. The strongest carrier on the route with a full sample, United Airlines, flew 967 at 85.6% on time.
United Airlines is the most reliable of the three carriers covered here at 85.6% on time across 967 flights.
Key figures
On time
73.4%
Arrivals under 15 minutes late, of 1,061 completed flights
Avg delay
54 min
Across delayed arrivals only, not all flights
Cancelled
1.11%
National rate is 1.81%
Whole route
77.6%
Every carrier on ATL to DEN, 5,589 flights
These figures cover 1,079 flights between July 2025 and June 2026. Beyond the headline rate, 8.8% 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
Southwest against every carrier on ATL to DEN
Southwest flew 1,079 of the 5,589 flights on ATL to DEN, about 19% of it. Its 73.4% on time is 4 points worse than the route as a whole, which runs 77.6%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from United at 85.6% to Frontier at 70.9%.
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 (this page) | 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
When Southwest runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 36 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am217 flights90.1%
- 8am–11am128 flights85.9%
- 11am–2pm175 flights82.2%
- 2pm–5pm199 flights72.6%
- 5pm–8pm300 flights53.7%
- 8pm–5am60 flights63.2%
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 53.7% on time, against 90.1% 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 5pm–8pm window is the busiest, with 300 flights scheduled in it.
Across the year
Southwest on ATL to DEN through the year
August is the worst month at 60.9% on time, 28 points below January, the best at 88.5%. 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. March was the busiest month here, with 93 flights.
Across the week, Tuesday is the strongest day at 80.9% on time and Sunday the weakest at 64.5%. 16 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
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 15,000 reported delay minutes.
- 41%Late-arriving aircraft
- 27%National Airspace System
- 27%Carrier
- 4%Extreme weather
- 1%Security
41% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 15,000 reported delay minutes here, that single category outweighs weather by 10 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 15,253 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 90.1% on time here.
Cancellations sit at 1.11% against a national 1.81%, which is ordinary. Diversions add another 0.56%.
Connections and stage length
What a delay here costs
8.8% 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 last about 55 minutes, 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 66.3% on time across 1,080 flights, 7 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 7 points of difference.
One caution: this is a thin sample. 1,079 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.
What to do with this
Booking Southwest on ATL to DEN
Put together: treat all of this as provisional. 1,079 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 73.4% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 1,061 completed flights over 12 months sit behind that.
Related
Where to go next
- ATL to DEN, every carrier
- Southwest on DEN to ATL, the return leg
- United Airlines on ATL to DEN85.6%
- Delta Air Lines on ATL to DEN78.1%
- Frontier Airlines on ATL to DEN70.9%
- Southwest Airlines network-wide record
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Denver International (DEN) delay statistics
- Why the first flight of the morning is statistically safest
- Same route, different airline: where the carrier you pick matters most
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.