Route reliability record
STL→MIA
St. Louis to Miami
- Flights
- 1,144
- Period
- July 2025 to June 2026
- Distance
- 1,068 mi
- Carriers
- 4
This route lands a B+, 5 points better than the national rate of 77.6%. About one flight in six arrives 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 1,144 STL to MIA flights, of which American Airlines flew 605 at 88.6% on time.
Best time to fly STL to MIA: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 91.7% of the time and Wednesday flights 92.7%, against 82.8% for the route overall.
Set against the rest of the country, this route's record is 5 points better than the US average of 77.6%. That gap is worth roughly 52 fewer late arrivals for every thousand flights.
Key figures
On time
82.8%
Arrivals under 15 minutes late, of 1,133 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
0.70%
National rate is 1.81%
Best carrier
American
88.6% on time across 605 flights
These figures cover 1,144 flights between July 2025 and June 2026. The median arrival is 9 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 STL to MIA
The choice of carrier is not cosmetic here. American Airlines arrives on time 88.6% of the time; Southwest Airlines manages 75.6%. Sample sizes sit next to every figure, because a two-point gap across 442 flights means less than a ten-point one.
| 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 | 442 | 75.6% | 43 min | 0.45% | B+ |
| Republic Airwaysthin sample | 4 | 25.0% | 36 min | 0.00% | F+ |
The spread between American and Southwest is 13 points, wide enough that it should decide the booking. On a hundred trips that is 13 more arrivals inside the on-time window.
Best ways to make this trip
The most reliable ways to fly St. Louis to Miami
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 1 of the top 3 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. STL → MIASt. Louis to Miami | American Airlines | 87.7% | 88.6% | 0.99% | 5am–8am, Wed | — |
| 2. STL → MIASt. Louis to Miami | Southwest Airlines | 75.3% | 75.6% | 0.45% | 8am–11am, Wed | — |
| 3. STL → FLLSt. Louis to Fort Lauderdale | Southwest Airlines | 73.8% | 74.1% | 0.39% | 5am–8am, Wed (route) | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 19 points, against 13 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am377 flights91.7%
- 8am–11am206 flights82.0%
- 11am–2pm278 flights81.2%
- 2pm–5pm87 flights72.4%
- 5pm–8pm174 flights75.6%
- 8pm–5am22 flights—
Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 91.7% of the time, against 72.4% for the afternoon window. That is 19 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 377 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 20 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.
June is the worst month at 73.7% on time, 20 points below April, the best at 93.8%. 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 136 flights.
Across the week, Wednesday is the strongest day at 92.7% on time and Saturday the weakest at 70.1%. 23 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 12,000 reported delay minutes.
- 41%Late-arriving aircraft
- 30%Carrier
- 23%National Airspace System
- 7%Extreme weather
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 12,000 reported delay minutes here, that single category outweighs weather by 6 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 11,908 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 91.7% on time here.
Cancellations are rare at 0.70%, 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 actually costs
5.1% 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 an hour, 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 72.4% on time across 1,141 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.
The sample behind these figures is 1,144 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.
Work out the risk of missing a connection in MIA after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 93.8% on time and June 73.7%, a swing of 20 points. If the dates move at all, move them out of June before you think about anything else. 1,133 completed flights over 12 months sit behind that.
Common questions
STL to MIA questions
How often is STL to MIA delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 17.2% of the 1,144 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on STL to MIA?
American Airlines leads at 88.6% on time across 605 flights. Southwest Airlines is at the other end on 75.6%, a gap of 13 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 STL to MIA?
The 5am–8am departure window is the strongest at 91.7% on time. The 2pm–5pm window is the weakest at 72.4%, 19 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 June delays on STL to MIA?
June is the weakest month at 73.7% on time, compared with 93.8% in April. Across the year that is 20 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
- MIA to STL — the return legseparate record
- St. Louis Lambert International (STL) delay statistics
- Miami International (MIA) delay statistics
- American Airlines on STL to MIA88.6%
- Southwest Airlines on STL to MIA75.6%
- STL to ATL, a related route85.3%
- ATL to MIA, a related route71.0%
- STL to DEN, a related route74.9%
- American Airlines on-time record88.6%
- Envoy Air on-time record81.7%
- Southwest Airlines on-time record75.6%
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
Direction matters. STL to MIA and MIA to STL are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.