Carrier route record
WNSTL→MIA
Southwest Airlines · St. Louis to Miami
- Flights
- 442
- Period
- July 2025 to June 2026
- Share of route
- 39%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on STL to MIA sits in the middle of the pack with a B+. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.6%. The late ones land roughly 45 minutes behind schedule. That rests on 442 flights, with a median arrival right on schedule.
The US average over the same twelve months is 77.6%, so there is little to separate Southwest on STL to MIA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
75.6%
Arrivals under 15 minutes late, of 438 completed flights
Avg delay
43 min
Across delayed arrivals only, not all flights
Cancelled
0.45%
National rate is 1.81%
Whole route
82.8%
Every carrier on STL to MIA, 1,144 flights
These figures cover 442 flights between July 2025 and June 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.
Carrier by carrier
Southwest against every carrier on STL to MIA
Southwest flew 442 of the 1,144 flights on STL to MIA, about 39% of it. Its 75.6% on time is 7 points worse than the route as a whole, which runs 82.8%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from American at 88.6% to Republic at 25.0%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 605 | 88.6% | 94 min | 0.99% | A+ |
| Envoy Airthin sample | 93 | 81.7% | 47 min | 0.00% | B+ |
| Southwest Airlines (this page) | 442 | 75.6% | 43 min | 0.45% | B+ |
| Republic Airwaysthin sample | 4 | 25.0% | 36 min | 0.00% | F+ |
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 12 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am10 flights—
- 8am–11am189 flights81.4%
- 11am–2pm142 flights75.7%
- 2pm–5pm52 flights69.2%
- 5pm–8pm27 flights—
- 8pm–5am22 flights—
Scale runs 60% to 85%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 81.4% of the time, against 69.2% for the afternoon window. That is 12 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 189 flights scheduled in it.
Across the year
Southwest on STL to MIA through the year
June is the worst month at 53.8% on time, 31 points below April, the best at 84.8%. 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 43 flights.
Across the week, Wednesday is the strongest day at 94.1% on time and Saturday the weakest at 61.8%. 32 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 4,618 reported delay minutes.
- 37%National Airspace System
- 35%Late-arriving aircraft
- 24%Carrier
- 4%Extreme weather
35% 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 4,618 reported delay minutes here, that single category outweighs weather by 9 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 4,618 reported delay minutes.
37% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 1,714 minutes out of 4,618, against a national NAS share of 21%.
Cancellations are rare at 0.45%, 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
5.5% 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 roughly 45 minutes, which a normal layover absorbs.
The 1,068 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 66.9% on time across 441 flights, 9 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 9 points of difference.
One caution: this is a thin sample. 442 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 STL to MIA
Put together: treat all of this as provisional. 442 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 75.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 438 completed flights over 12 months sit behind that.
Related
Where to go next
- STL to MIA, every carrier
- Southwest on MIA to STL, the return leg
- American Airlines on STL to MIA88.6%
- Southwest Airlines network-wide record
- St. Louis Lambert International (STL) 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 7.04 million flight records
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.