Carrier route record
WNDEN→MIA
Southwest Airlines · Denver to Miami
- Flights
- 323
- Period
- September 2025 to August 2026
- Share of route
- 13%
- Carriers
- 4
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on DEN to MIA draws a D+. About one flight in three arrives at least 15 minutes late, and the typical late arrival is roughly 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 890 at 77.8% on time.
The national on-time rate over the same period is 77.3%, so Southwest on DEN to MIA runs 13 points behind the country as a whole. Across a thousand flights that is about 128 extra late arrivals.
Key figures
On time
64.5%
Arrivals under 15 minutes late, of 318 completed flights
Avg delay
48 min
Across delayed arrivals only, not all flights
Cancelled
0.62%
National rate is 1.89%
Whole route
74.9%
Every carrier on DEN to MIA, 2,443 flights
These figures cover 323 flights between September 2025 and August 2026. Beyond the headline rate, 8.8% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Southwest against every carrier on DEN to MIA
Southwest flew 323 of the 2,443 flights on DEN to MIA, about 13% of it. Its 64.5% on time is 10 points worse than the route as a whole, which runs 74.9%. Ranked by on-time rate it is last of four carriers on the route, where the range runs from American at 77.8% to Southwest at 64.5%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: 2 points 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 | 890 | 77.8% | 96 min | 1.01% | B |
| United Airlines | 877 | 76.3% | 60 min | 0.00% | B+ |
| Frontier Airlinesthin sample | 353 | 73.9% | 63 min | 0.28% | C+ |
| Southwest Airlines (this page)thin sample | 323 | 64.5% | 48 min | 0.62% | D+ |
No carrier stands out. American tops the table at 77.8%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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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 10 points, against 2 points between the best and worst carrier.
- 5am–8am6 flights—
- 8am–11am97 flights73.4%
- 11am–2pm184 flights63.2%
- 2pm–5pm22 flights—
- 5pm–8pm13 flights—
- 8pm–5am1 flights—
Scale runs 55% to 80%. 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 63.2% on time against 73.4% for 8am–11am. 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 184 flights scheduled in it.
Across the year
Southwest on DEN to MIA through the year
- Jul–Sep 202517 flights—
- Oct–Dec 202587 flights70.9%
- Jan–Mar 202695 flights60.9%
- Apr–Jun 202674 flights62.2%
- Jul–Sep 202650 flights61.2%
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 64.5% 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 Jan–Mar 2026 at 60.9%, a swing of 10 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 76.9% on time and Friday the weakest at 52.9%, a spread of 24 points.
Arrival by arrival
How late Southwest on DEN to MIA runs when it is late
The 113 late arrivals split 52 under half an hour, 33 between 30 and 60 minutes, and 28 an hour or more.
- 15+ min early23 flights7.2%
- Within 15 min182 flights57.2%
- 15–29 min late52 flights16.4%
- 30–59 min late33 flights10.4%
- 1–2 hours late19 flights6.0%
- 2+ hours late9 flights2.8%
Scale runs 0% to 100%.
Share of 318 completed flights by arrival against schedule.
28 of 104 late departures made up the time and arrived on time, 27% of them. In the other direction, 37 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at MIA.
The worst days
Worst days for Southwest on DEN to MIA
The latest arrival of the period was on 8 March 2026, 4 hours 40 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The five worst days are spread across March, December and February, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 8 March 2026 | 4 hours 40 minutes | Carrier |
| 19 December 2025 | 3 hours 45 minutes | Late-arriving aircraft |
| 6 March 2026 | 3 hours 2 minutes | Late-arriving aircraft |
| 20 February 2026 | 2 hours 28 minutes | Carrier |
| 26 December 2025 | 2 hours 22 minutes | National Airspace System |
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 5,429 reported delay minutes.
- 35%Carrier
- 33%Late-arriving aircraft
- 32%National Airspace System
The largest share of delay minutes, 35%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 1,910 of the 5,429 delay minutes reported here. The split is drawn from 5,429 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 73.4% on time here.
Cancellations are rare at 0.62%, below the national 1.89% 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
8.8% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last roughly 50 minutes, which a normal layover absorbs.
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 54.5% on time across 323 flights, 10 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 10 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 64.5% 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 MIA77.8%
- United Airlines on DEN to MIA76.3%
- Frontier Airlines on DEN to MIA73.9%
- Southwest Airlines network-wide record
- Denver International (DEN) delay statistics
- Miami International (MIA) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.