Carrier route record
F9MIA→SJU
Frontier Airlines · Miami to San Juan
- Flights
- 379
- Period
- July 2025 to June 2026
- Share of route
- 14%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Frontier Airlines.
Frontier on MIA to SJU sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 6 points worse than the national rate of 77.6%. The late ones land an hour and a half behind schedule. That rests on 379 flights, with a median arrival 4 minutes early.
The national on-time rate over the same period is 77.6%, so Frontier on MIA to SJU runs 6 points behind the country as a whole. Across a thousand flights that is about 61 extra late arrivals.
Key figures
On time
71.5%
Arrivals under 15 minutes late, of 372 completed flights
Avg delay
85 min
Across delayed arrivals only, not all flights
Cancelled
1.85%
National rate is 1.81%
Whole route
74.7%
Every carrier on MIA to SJU, 2,636 flights
These figures cover 379 flights between July 2025 and June 2026. Beyond the headline rate, 13.4% 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
Frontier against every carrier on MIA to SJU
Frontier flew 379 of the 2,636 flights on MIA to SJU, about 14% of it. Its 71.5% on time is 3 points worse than the route as a whole, which runs 74.7%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from American at 76.8% to Spirit at 55.8%. One 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 | 2,078 | 76.8% | 71 min | 0.53% | B+ |
| Frontier Airlines (this page) | 379 | 71.5% | 85 min | 1.85% | C |
| Spirit Airlinesthin sample | 179 | 55.8% | 96 min | 3.91% | D− |
Departure window
When Frontier runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 27 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–8am71 flights76.8%
- 8am–11am44 flights83.7%
- 11am–2pm15 flights—
- 2pm–5pm92 flights75.8%
- 5pm–8pm44 flights56.8%
- 8pm–5am113 flights64.5%
Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 56.8% on time, against 83.7% for the 8am–11am 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 113 flights scheduled in it.
Across the year
Frontier on MIA to SJU through the year
July is the worst month at 60.0% on time, 15 points below January, the best at 75.0%. 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. December was the busiest month here, with 44 flights.
Across the week, Wednesday is the strongest day at 84.4% on time and Saturday the weakest at 56.4%. 28 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Frontier runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 51% of the 8,952 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.
- 51%Late-arriving aircraft
- 24%National Airspace System
- 23%Carrier
- 2%Extreme weather
51% 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 8,952 reported delay minutes here, that single category outweighs weather by 30 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 8,952 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 83.7% on time here.
Cancellations sit at 1.85% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 13.4% 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 76.5% on time across 379 flights, 5 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 5 points of difference.
One caution: this is a thin sample. 379 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 Frontier on MIA to SJU
Put together: treat all of this as provisional. 379 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 71.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 372 completed flights over 12 months sit behind that.
Related
Where to go next
- MIA to SJU, every carrier
- Frontier on SJU to MIA, the return leg
- American Airlines on MIA to SJU76.8%
- Spirit Airlines on MIA to SJU55.8%
- Frontier Airlines network-wide record
- Miami International (MIA) delay statistics
- Luis Munoz Marin International (SJU) 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.