Route reliability record
MIA→STL
Miami to St. Louis
- Flights
- 1,141
- Period
- July 2025 to June 2026
- Distance
- 1,068 mi
- Carriers
- 4
This route sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 5 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 1,141 MIA to STL flights, of which American Airlines flew 603 at 73.8% on time.
Best time to fly MIA to STL: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 93.9% of the time and Wednesday flights 78.8%, against 72.4% for the route overall.
The national on-time rate over the same period is 77.6%, so this route runs 5 points behind the country as a whole. Across a thousand flights that is about 52 extra late arrivals.
Key figures
On time
72.4%
Arrivals under 15 minutes late, of 1,130 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
0.70%
National rate is 1.81%
Best carrier
American
73.8% on time across 603 flights
These figures cover 1,141 flights between July 2025 and June 2026. Beyond the headline rate, 10.9% 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
Which airline is most reliable on MIA to STL
The choice of carrier is not cosmetic here. American Airlines arrives on time 73.8% of the time; Southwest Airlines manages 66.9%. Sample sizes sit next to every figure, because a two-point gap across 441 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Envoy Airthin sample | 93 | 89.2% | 47 min | 0.00% | A+ |
| Republic Airwaysthin sample | 4 | 75.0% | 196 min | 0.00% | B+ |
| American Airlines | 603 | 73.8% | 73 min | 1.00% | C |
| Southwest Airlines | 441 | 66.9% | 60 min | 0.45% | C+ |
American leads Southwest by 7 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Best ways to make this trip
The most reliable ways to fly Miami to St. Louis
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. FLL → STLFort Lauderdale to St. Louis | Southwest Airlines | 77.9% | 78.2% | 0.39% | 5am–8am, Tue (route) | — |
| 2. MIA → STLMiami to St. Louis | American Airlines | 73.1% | 73.8% | 1.00% | 8am–11am, Wed | — |
| 3. MIA → STLMiami to St. Louis | Southwest Airlines | 66.6% | 66.9% | 0.45% | 5am–8am, Sat | — |
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 43 points, against 7 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am82 flights93.9%
- 8am–11am160 flights90.6%
- 11am–2pm52 flights84.3%
- 2pm–5pm285 flights76.2%
- 5pm–8pm187 flights51.4%
- 8pm–5am375 flights65.8%
Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 51.4% on time, against 93.9% 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 8pm–5am window is the busiest, with 375 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 30 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.
August is the worst month at 53.4% on time, 30 points below November, the best at 82.9%. 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 78.8% on time and Sunday the weakest at 62.3%. 17 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Late-arriving aircraft accounts for 53% of the 21,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 53%Late-arriving aircraft
- 33%Carrier
- 11%National Airspace System
- 3%Extreme weather
- 0%Security
53% 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 21,000 reported delay minutes here, that single category outweighs weather by 21 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 20,673 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 93.9% 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
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 10.9% 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.
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 82.8% on time across 1,144 flights, 10 points above 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 1,141 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 STL 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. November runs 82.9% on time and August 53.4%, a swing of 30 points. If the dates move at all, move them out of August before you think about anything else. 1,130 completed flights over 12 months sit behind that.
Common questions
MIA to STL questions
How often is MIA to STL delayed?
Roughly one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 27.6% of the 1,141 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on MIA to STL?
American Airlines leads at 73.8% on time across 603 flights. Southwest Airlines is at the other end on 66.9%, a gap of 7 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 MIA to STL?
The 5am–8am departure window is the strongest at 93.9% on time. The 5pm–8pm window is the weakest at 51.4%, 43 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 August delays on MIA to STL?
August is the weakest month at 53.4% on time, compared with 82.9% in November. Across the year that is 30 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
- STL to MIA — the return legseparate record
- Miami International (MIA) delay statistics
- St. Louis Lambert International (STL) delay statistics
- American Airlines on MIA to STL73.8%
- Southwest Airlines on MIA to STL66.9%
- MIA to ATL, a related route73.7%
- ATL to STL, a related route82.4%
- MIA to LGA, a related route68.0%
- Envoy Air on-time record89.2%
- Republic Airways on-time record75.0%
- American Airlines on-time record73.8%
- Why the first flight of the morning is statistically safest
- How often a connection fails at the major US hubs
Direction matters. MIA to STL and STL to MIA 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.