Carrier route record
DLBOS→MIA
Delta Air Lines · Boston to Miami
- Flights
- 890
- Period
- July 2025 to June 2026
- Share of route
- 26%
- Carriers
- 5
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on BOS to MIA 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 a little over an hour behind schedule. That rests on 890 flights, with a median arrival 2 minutes early.
The national on-time rate over the same period is 77.6%, so Delta on BOS to MIA runs 6 points behind the country as a whole. Across a thousand flights that is about 55 extra late arrivals.
Key figures
On time
72.1%
Arrivals under 15 minutes late, of 865 completed flights
Avg delay
76 min
Across delayed arrivals only, not all flights
Cancelled
2.70%
National rate is 1.81%
Whole route
77.7%
Every carrier on BOS to MIA, 3,417 flights
These figures cover 890 flights between July 2025 and June 2026. Beyond the headline rate, 10.8% 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
Delta against every carrier on BOS to MIA
Delta flew 890 of the 3,417 flights on BOS to MIA, about 26% of it. Its 72.1% on time is 6 points worse than the route as a whole, which runs 77.7%. Ranked by on-time rate it is number three of five carriers on the route, where the range runs from American at 82.3% to Republic at 47.6%. Three 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 | 2,231 | 82.3% | 74 min | 1.75% | B |
| JetBlue Airwaysthin sample | 88 | 72.6% | 71 min | 3.41% | C− |
| Delta Air Lines (this page) | 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+ |
Flight by flight
Delta flight numbers on BOS to MIA
Departure window
When Delta runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 23 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–8am364 flights85.4%
- 8am–11am2 flights—
- 11am–2pm17 flights—
- 2pm–5pm351 flights62.1%
- 5pm–8pm3 flights—
- 8pm–5am153 flights64.8%
Scale runs 55% to 90%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 85.4% of the time, against 62.1% for the afternoon window. That is 23 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 364 flights scheduled in it.
Across the year
Delta on BOS to MIA through the year
December is the weak month at 58.8% on time, against 85.2% in August. 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. March was the busiest month here, with 93 flights.
Across the week, Monday is the strongest day at 76.9% on time and Sunday the weakest at 60.3%. 17 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Delta runs late on this route
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 18,000 reported delay minutes.
- 41%Carrier
- 34%Late-arriving aircraft
- 25%National Airspace System
- 1%Extreme weather
The largest share of delay minutes, 41%, 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 7,576 of the 18,000 delay minutes reported here. The split is drawn from 18,406 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 85.4% on time here.
Cancellations run at 2.70%, against 1.81% nationally. That is about one flight in 40 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.
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. 10.8% 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 runs 70.0% on time across 888 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
One caution: this is a thin sample. 890 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 Delta on BOS to MIA
Put together: treat all of this as provisional. 890 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 72.1% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 865 completed flights over 12 months sit behind that.
Related
Where to go next
- BOS to MIA, every carrier
- Delta on MIA to BOS, the return leg
- American Airlines on BOS to MIA82.3%
- Spirit Airlines on BOS to MIA54.0%
- Delta Air Lines network-wide record
- Boston Logan International (BOS) delay statistics
- Miami International (MIA) delay statistics
- The US routes with the most cancellations
- Why the first flight of the morning is statistically safest
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.