Route reliability record

BOS→MIA

Boston to Miami

Flights: 3,417
Period: July 2025 to June 2026
Distance: 1,258 mi
Carriers: 5

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 a little over an hour on average. That is a workable record, not a spotless one. That rests on 3,417 flights, of which American Airlines flew 2,231 at 82.3% 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 3,332 completed flights

Avg delay

75 min

Across delayed arrivals only, not all flights

Cancelled

2.25%

National rate is 1.81%

Best carrier

American

82.3% on time across 2,231 flights

These figures cover 3,417 flights between July 2025 and June 2026. Beyond the headline rate, 8.9% 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 BOS to MIA

The choice of carrier is not cosmetic here. American Airlines arrives on time 82.3% of the time; Delta Air Lines manages 72.1%. Sample sizes sit next to every figure, because a two-point gap across 890 flights means less than a ten-point one.

On-time performance by carrier on BOS to MIA
Airline	Flights	On time	Avg delay	Cancelled	Grade
American Airlines	2,231	82.3%	74 min	1.75%	B
JetBlue Airwaysthin sample	88	72.6%	71 min	3.41%	C−
Delta Air Lines	890	72.1%	76 min	2.70%	C
Spirit Airlinesthin sample	187	54.0%	82 min	5.88%	F−
Republic Airwaysthin sample	21	47.6%	50 min	0.00%	F+

American leads Delta by 10 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

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

5am–8am1,250 flights91.1%
8am–11am315 flights83.1%
11am–2pm536 flights76.9%
2pm–5pm703 flights63.1%
5pm–8pm453 flights66.1%
8pm–5am160 flights62.9%

Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 62.9% on time, against 91.1% 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 5am–8am window is the busiest, with 1,250 flights scheduled in it.

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.

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

December is the weak month at 69.9% on time, against 86.7% in June. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. April was the busiest month here, with 334 flights.

Across the week, Wednesday is the strongest day at 83.4% on time and Sunday the weakest at 69.2%. 14 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 56,000 reported delay minutes.

Carrier
37%
Late-arriving aircraft
32%
National Airspace System
29%
Extreme weather
2%
Security
0%

The largest share of delay minutes, 37%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 21,000 of the 56,000 delay minutes reported here. The split is drawn from 55,709 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 91.1% on time here.

Cancellations sit at 2.25% against a national 1.81%, which is ordinary. Diversions add another 0.23%.

Connections and stage length

What a delay here actually costs

8.9% of arrivals land an hour or more late, close to the national 8.1%. 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 are the a little over an hour kind, which a normal layover absorbs.

The 1,258 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 69.7% on time across 3,415 flights, 8 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 8 points of difference.

The sample behind these figures is 3,417 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 86.7% on time and December 69.9%, a swing of 17 points. If the dates move at all, move them out of December before you think about anything else. 3,332 completed flights over 12 months sit behind that.

Common questions

BOS to MIA questions

How often is BOS 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 3,417 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on BOS to MIA?

American Airlines leads at 82.3% on time across 2,231 flights. Delta Air Lines is at the other end on 72.1%, a gap of 10 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 BOS to MIA?

The 5am–8am departure window is the strongest at 91.1% on time. The 8pm–5am window is the weakest at 62.9%, 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 December delays on BOS to MIA?

December is the weakest month at 69.9% on time, compared with 86.7% in June. 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.

Where to go next

Direction matters. BOS to MIA and MIA to BOS 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