Route reliability record
MIA→SJU
Miami to San Juan
- Flights
- 2,645
- Period
- September 2025 to August 2026
- Distance
- 1,045 mi
- Carriers
- 3
This route lands a B+, about a point worse than the national rate of 77.3%. About one flight in four arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That rests on 2,645 MIA to SJU flights, of which American Airlines flew 2,140 at 78.2% on time.
Best time to fly MIA to SJU: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 91.3% of the time and Wednesday flights 85.1%, against 76.3% for the route overall.
The US average over the same twelve months is 77.3%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
76.3%
Arrivals under 15 minutes late, of 2,620 completed flights
Avg delay
73 min
Across delayed arrivals only, not all flights
Cancelled
0.87%
National rate is 1.89%
Best carrier
American
78.2% on time across 2,140 flights
These figures cover 2,645 flights between September 2025 and August 2026. Beyond the headline rate, 8.9% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Which airline is most reliable on MIA to SJU
The choice of carrier is not cosmetic here. American Airlines arrives on time 78.2% of the time; Frontier Airlines manages 71.8%. Sample sizes sit next to every figure, because a two-point gap across 381 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 2,140 | 78.2% | 68 min | 0.51% | B+ |
| Frontier Airlines | 381 | 71.8% | 77 min | 1.31% | C |
| Spirit Airlinesthin sample | 124 | 56.4% | 101 min | 5.65% | D− |
American leads Frontier by 6 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
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Best ways to make this trip
The most reliable ways to fly Miami to San Juan
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. MIA → SJUMiami to San Juan | American Airlines | 77.8% | 78.2% | 0.51% | 5am–8am, Wed | — |
| 2. MIA → SJUMiami to San Juan | Frontier Airlines | 70.9% | 71.8% | 1.31% | 8am–11am, Wed | — |
| 3. FLL → SJUFort Lauderdale to San Juan | JetBlue Airways | 68.2% | 69.3% | 1.57% | 5am–8am, Tue | B6 553 17:45 |
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 29 points, against 6 points between the best and worst carrier.
- 5am–8am372 flights91.3%
- 8am–11am629 flights87.0%
- 11am–2pm525 flights72.9%
- 2pm–5pm517 flights70.7%
- 5pm–8pm274 flights65.1%
- 8pm–5am328 flights62.4%
Scale runs 55% to 95%.
The 8pm–5am window is where this operation falls apart: 62.4% on time, against 91.3% 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 8am–11am window is the busiest, with 629 flights scheduled in it.
Explore
Filter MIA to SJU by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On MIA to SJU, the best departure window is 5am–8am at 91.3% on time and the worst is 8pm–5am at 62.4%, a wide gap of 28.9 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am91.3%
- 8–11am87.0%
- 11am–2pm72.9%
- 2–5pm70.7%
- 5–8pm65.1%
- 8pm–5am62.4%
best all US flightsScale 55% to 95%.
Across the year
When delays peak on this route
This route's year swings by 17 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.
May is the best month on the calendar at 85.5% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. March was the busiest month here, with 278 flights.
Across the week, Wednesday is the strongest day at 85.1% on time and Sunday the weakest at 67.8%, a spread of 17 points.
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 45,000 reported delay minutes.
- 40%Late-arriving aircraft
- 39%Carrier
- 17%National Airspace System
- 4%Extreme weather
- 0%Security
40% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 45,000 reported delay minutes here, that single category outweighs weather by 10 to one. The split is drawn from 45,025 reported delay minutes.
The largest share of delay minutes, 39%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 18,000 of the 45,000 delay minutes reported here.
Cancellations are rare at 0.87%, 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 actually costs
8.9% 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 a little over an hour, which a normal layover absorbs.
The 1,045 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.
The return leg runs 78.9% on time across 2,650 flights, within 3 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
The sample behind these figures is 2,645 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 SJU 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. May runs 85.5% on time and March 68.2%, a swing of 17 points. If the dates move at all, move them out of March before you think about anything else. 2,620 completed flights over 12 months sit behind that.
Common questions
MIA to SJU questions
How often is MIA to SJU delayed?
About 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 23.7% of the 2,645 flights in this analysis, against 22.7% nationally. Delayed flights are late by a little over an hour on average.
Which airline is most reliable on MIA to SJU?
American Airlines leads at 78.2% on time across 2,140 flights. Frontier Airlines is at the other end on 71.8%, a gap of 6 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 SJU?
The 5am–8am departure window is the strongest at 91.3% on time. The 8pm–5am window is the weakest at 62.4%, 29 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 March delays on MIA to SJU?
March is the weakest month at 68.2% on time, compared with 85.5% in May. Across the year that is 17 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
- SJU to MIA — the return legseparate record
- Miami International (MIA) delay statistics
- Luis Munoz Marin International (SJU) delay statistics
- American Airlines on MIA to SJU78.2%
- Frontier Airlines on MIA to SJU71.8%
- Spirit Airlines on MIA to SJU56.4%
- MIA to ATL, a related route74.2%
- MCO to SJU, a related route73.8%
- MIA to LGA, a related route67.4%
- American Airlines on-time record78.2%
- Frontier Airlines on-time record71.8%
- Spirit Airlines on-time record56.4%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. MIA to SJU and SJU 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.