Route reliability record

MIA→BOS

Miami to Boston

Flights: 3,415
Period: July 2025 to June 2026
Distance: 1,258 mi
Carriers: 6

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, 8 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 3,415 flights, of which American Airlines flew 2,230 at 70.7% on time.

The national on-time rate over the same period is 77.6%, so this route runs 8 points behind the country as a whole. Across a thousand flights that is about 79 extra late arrivals.

On time

69.7%

Arrivals under 15 minutes late, of 3,327 completed flights

Avg delay

73 min

Across delayed arrivals only, not all flights

Cancelled

2.40%

National rate is 1.81%

Best carrier

American

70.7% on time across 2,230 flights

These figures cover 3,415 flights between July 2025 and June 2026. Beyond the headline rate, 12.4% 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 MIA to BOS

The two carriers here are closely matched: half a point 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 MIA to BOS
Airline	Flights	On time	Avg delay	Cancelled	Grade
Envoy Airthin sample	1	100.0%	—	0.00%	A+
Republic Airwaysthin sample	21	81.0%	96 min	0.00%	B+
American Airlines	2,230	70.7%	71 min	1.75%	C
Delta Air Lines	888	70.0%	78 min	2.93%	C
JetBlue Airwaysthin sample	89	66.7%	68 min	5.62%	C−
Spirit Airlinesthin sample	186	54.3%	70 min	6.45%	F−

No carrier stands out. American tops the table at 70.7%, half a point 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 29 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–8am345 flights87.4%
8am–11am588 flights86.2%
11am–2pm772 flights68.3%
2pm–5pm225 flights67.9%
5pm–8pm563 flights58.5%
8pm–5am922 flights60.8%

Scale runs 50% to 95%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 58.5% on time, against 87.4% 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 922 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 21 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.May best, October worst

May is the best month on the calendar at 77.4% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. April was the busiest month here, with 333 flights.

Across the week, Saturday is the strongest day at 74.7% on time and Sunday the weakest at 63.6%. 11 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 74,000 reported delay minutes.

Late-arriving aircraft
41%
Carrier
32%
National Airspace System
23%
Extreme weather
3%
Security
0%

41% 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 74,000 reported delay minutes here, that single category outweighs weather by 13 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 73,512 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 87.4% on time here.

Cancellations sit at 2.40% against a national 1.81%, which is ordinary. Diversions add another 0.18%.

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. 12.4% 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 1,258 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 77.7% on time across 3,417 flights, 8 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 8 points of difference.

The sample behind these figures is 3,415 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. May runs 77.4% on time and October 56.9%, a swing of 21 points. If the dates move at all, move them out of October before you think about anything else. 3,327 completed flights over 12 months sit behind that.

Common questions

MIA to BOS questions

How often is MIA to BOS delayed?

Roughly one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 30.3% of the 3,415 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 MIA to BOS?

American Airlines leads at 70.7% on time across 2,230 flights. Delta Air Lines is at the other end on 70.0%, a gap of half a point. 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 BOS?

The 5am–8am departure window is the strongest at 87.4% on time. The 5pm–8pm window is the weakest at 58.5%, 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 October delays on MIA to BOS?

October is the weakest month at 56.9% on time, compared with 77.4% in May. Across the year that is 21 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. MIA to BOS and BOS to MIA 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