Carrier route record
DLMIA→BOS
Delta Air Lines · Miami to Boston
- Flights
- 888
- Period
- July 2025 to June 2026
- Share of route
- 26%
- Carriers
- 6
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on MIA to BOS 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 888 flights, with a median arrival 3 minutes early.
The national on-time rate over the same period is 77.6%, so Delta on MIA to BOS runs 8 points behind the country as a whole. Across a thousand flights that is about 76 extra late arrivals.
Key figures
On time
70.0%
Arrivals under 15 minutes late, of 860 completed flights
Avg delay
78 min
Across delayed arrivals only, not all flights
Cancelled
2.93%
National rate is 1.81%
Whole route
69.7%
Every carrier on MIA to BOS, 3,415 flights
These figures cover 888 flights between July 2025 and June 2026. Beyond the headline rate, 12.0% 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 MIA to BOS
Delta flew 888 of the 3,415 flights on MIA to BOS, about 26% of it. Its 70.0% on time is about level with the route as a whole at 69.7%. Ranked by on-time rate it is number four of six carriers on the route, where the range runs from Envoy at 100.0% to Spirit at 54.3%. Four 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 |
|---|---|---|---|---|---|
| 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 (this page) | 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− |
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 30 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–8am156 flights82.7%
- 8am–11am8 flights—
- 11am–2pm365 flights73.1%
- 2pm–5pm3 flights—
- 5pm–8pm64 flights53.1%
- 8pm–5am292 flights62.7%
Scale runs 45% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 53.1% on time, against 82.7% 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 11am–2pm window is the busiest, with 365 flights scheduled in it.
Across the year
Delta on MIA to BOS through the year
May is the best month on the calendar at 79.1% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. March was the busiest month here, with 93 flights.
Across the week, Tuesday is the strongest day at 80.0% on time and Sunday the weakest at 63.9%. 16 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 20,000 reported delay minutes.
- 42%Carrier
- 35%Late-arriving aircraft
- 22%National Airspace System
- 2%Extreme weather
35% 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 20,000 reported delay minutes here, that single category outweighs weather by 20 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 20,079 reported delay minutes.
The largest share of delay minutes, 42%, 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 8,333 of the 20,000 delay minutes reported here.
Cancellations run at 2.93%, against 1.81% nationally. That is roughly one flight in 30 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. 12.0% 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 72.1% on time across 890 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. 888 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 MIA to BOS
Put together: the delay figures matter less here than the 2.93% cancellation rate. A late arrival costs you a little over an hour; a cancelled flight costs you the day. Book the 5am–8am departure so there is still a schedule behind you if it goes wrong, and treat a same-day connection as optimistic. 860 completed flights over 12 months sit behind that.
Related
Where to go next
- MIA to BOS, every carrier
- Delta on BOS to MIA, the return leg
- American Airlines on MIA to BOS70.7%
- Spirit Airlines on MIA to BOS54.3%
- Delta Air Lines network-wide record
- Miami International (MIA) delay statistics
- Boston Logan International (BOS) 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.