Carrier route record
WNDEN→MIA
Southwest Airlines · Denver to Miami
- Flights
- 323
- Period
- July 2025 to June 2026
- Share of route
- 13%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on DEN to MIA draws a D+. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is about 50 minutes behind schedule. Build slack into anything you connect to. That rests on 323 flights. The strongest carrier on the route with a full sample, American Airlines, flew 886 at 76.6% on time.
The national on-time rate over the same period is 77.6%, so Southwest on DEN to MIA runs 14 points behind the country as a whole. Across a thousand flights that is about 144 extra late arrivals.
Key figures
On time
63.2%
Arrivals under 15 minutes late, of 318 completed flights
Avg delay
51 min
Across delayed arrivals only, not all flights
Cancelled
0.62%
National rate is 1.81%
Whole route
74.0%
Every carrier on DEN to MIA, 2,490 flights
These figures cover 323 flights between July 2025 and June 2026. Beyond the headline rate, 10.4% 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 DEN to MIA
Southwest flew 323 of the 2,490 flights on DEN to MIA, about 13% of it. Its 63.2% on time is 11 points worse than the route as a whole, which runs 74.0%. Ranked by on-time rate it is last of four carriers on the route, where the range runs from American at 76.6% to Southwest at 63.2%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: about a point separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 886 | 76.6% | 102 min | 1.02% | B |
| United Airlines | 932 | 75.4% | 64 min | 0.11% | B+ |
| Frontier Airlinesthin sample | 349 | 73.6% | 59 min | 1.15% | C |
| Southwest Airlines (this page)thin sample | 323 | 63.2% | 51 min | 0.62% | D+ |
No carrier stands out. American tops the table at 76.6%, about a point clear of the bottom, which is inside the range this kind of sample moves year to year.
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 28 points, against about a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am6 flights—
- 8am–11am109 flights75.2%
- 11am–2pm147 flights61.6%
- 2pm–5pm47 flights46.8%
- 5pm–8pm13 flights—
- 8pm–5am1 flights—
Scale runs 40% to 80%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 75.2% of the time, against 46.8% for the afternoon window. That is 28 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 147 flights scheduled in it.
Across the year
Southwest on DEN to MIA through the year
- Jul–Sep 202567 flights57.6%
- Oct–Dec 202587 flights70.9%
- Jan–Mar 202695 flights60.9%
- Apr–Jun 202674 flights62.2%
Scale runs 50% to 75%. Rows with fewer than 30 flights show a dash.
Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 63.2% on time across 323 flights.
Southwest on DEN to MIA did not run the same all year. Its best quarter was Oct–Dec 2025 at 70.9% on time and its weakest Jul–Sep 2025 at 57.6%, a swing of 13 points on roughly 81 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
Across the week, Monday is the strongest day at 74.5% on time and Sunday the weakest at 54.7%. 20 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 5,916 reported delay minutes.
- 41%Carrier
- 31%Late-arriving aircraft
- 27%National Airspace System
- 1%Extreme weather
The largest share of delay minutes, 41%, 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 2,420 of the 5,916 delay minutes reported here. The split is drawn from 5,916 reported delay minutes.
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 75.2% on time here.
Cancellations are rare at 0.62%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 10.4% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
At 1,709 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 59.7% on time across 323 flights, 4 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 4 points of difference.
One caution: this is a thin sample. 323 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 DEN to MIA
Put together: treat all of this as provisional. 323 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 63.2% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 318 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to MIA, every carrier
- Southwest on MIA to DEN, the return leg
- American Airlines on DEN to MIA76.6%
- United Airlines on DEN to MIA75.4%
- Frontier Airlines on DEN to MIA73.6%
- Southwest Airlines network-wide record
- Denver International (DEN) delay statistics
- Miami International (MIA) delay statistics
- The best time of day to fly, according to 7.04 million flight records
- How often a connection fails at the major US hubs
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.