Route reliability record

SJU→MIA

San Juan to Miami

Flights: 2,642
Period: July 2025 to June 2026
Distance: 1,045 mi
Carriers: 3

This route lands a B+, level with the national rate of 77.6%. Roughly one flight in four arrive 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 2,642 flights, of which American Airlines flew 2,079 at 78.5% on time.

The US average over the same twelve months is 77.6%, 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.

On time

77.7%

Arrivals under 15 minutes late, of 2,613 completed flights

Avg delay

94 min

Across delayed arrivals only, not all flights

Cancelled

0.95%

National rate is 1.81%

Best carrier

American

78.5% on time across 2,079 flights

These figures cover 2,642 flights between July 2025 and June 2026. Beyond the headline rate, 9.4% 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 SJU to MIA

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.

On-time performance by carrier on SJU to MIA
Airline	Flights	On time	Avg delay	Cancelled	Grade
American Airlines	2,079	78.5%	93 min	0.63%	B+
Frontier Airlines	379	76.5%	95 min	2.11%	B
Spirit Airlinesthin sample	184	71.1%	94 min	2.17%	C

No carrier stands out. American tops the table at 78.5%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.

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 28 points, against 2 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am437 flights93.5%
8am–11am241 flights86.9%
11am–2pm831 flights81.4%
2pm–5pm410 flights67.6%
5pm–8pm608 flights65.7%
8pm–5am115 flights71.4%

Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 93.5% of the time, against 65.7% for the evening window. That is 28 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 831 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 16 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.

Darker means more delays. Figures are on-time percentages.June best, July worst

July is the worst month at 71.6% on time, 16 points below June, the best at 87.4%. 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 278 flights.

Across the week, Wednesday is the strongest day at 83.9% on time and Sunday the weakest at 72.3%. 12 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 57% of the 55,000 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.

Late-arriving aircraft
57%
Carrier
33%
National Airspace System
8%
Extreme weather
2%
Security
0%

57% 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 55,000 reported delay minutes here, that single category outweighs weather by 26 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 54,509 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 93.5% on time here.

Cancellations sit at 0.95% against a national 1.81%, which is ordinary. Diversions add another 0.15%.

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. 9.4% 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 1,045 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. 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 74.7% on time across 2,636 flights, 3 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 3 points of difference.

The sample behind these figures is 2,642 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.

What to do with this

Booking this route

Put together: the calendar is the biggest lever here, not the carrier or the hour. June runs 87.4% on time and July 71.6%, a swing of 16 points. If the dates move at all, move them out of July before you think about anything else. 2,613 completed flights over 12 months sit behind that.

Common questions

SJU to MIA questions

How often is SJU to MIA delayed?

Roughly one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.3% of the 2,642 flights in this analysis, against 22.4% nationally. Delayed flights are late by an hour and a half on average.

Which airline is most reliable on SJU to MIA?

American Airlines leads at 78.5% on time across 2,079 flights. Frontier Airlines is at the other end on 76.5%, a gap of 2 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 SJU to MIA?

The 5am–8am departure window is the strongest at 93.5% on time. The 5pm–8pm window is the weakest at 65.7%, 28 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 July delays on SJU to MIA?

July is the weakest month at 71.6% on time, compared with 87.4% in June. Across the year that is 16 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. SJU to MIA and MIA to SJU are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures