Flight number record
DL 1399
Delta Air Lines · Boston to Miami
- Route
- BOS → MIA
- Departs
- 07:05
- Flights
- 345
- Period
- July 2025 to June 2026
Historical statistics for July 2025 to June 2026, not live status. For today’s DL 1399, check with Delta Air Lines.
DL 1399 earns a B. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.6%. When something does go wrong the average delay runs an hour and a half. That rests on 345 flights, with a median arrival 8 minutes early.
Set against the rest of the country, DL 1399's record is 7 points better than the US average of 77.6%. That gap is worth roughly 73 fewer late arrivals for every thousand flights.
Key figures
On time
84.9%
Arrivals under 15 minutes late, of 338 completed flights
Avg delay
84 min
Across delayed arrivals only, not all flights
Cancelled
2.03%
National rate is 1.81%
1 hour+ late
4.1%
National rate is 8.1%
These figures cover 345 flights between July 2025 and June 2026. The median arrival is 8 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Schedule
When DL 1399 flies
DL 1399 flies BOS to MIA without a single fixed slot. Its most common scheduled departure was 07:05, used on 96 of 345 flights, with 07:10 (70 flights) and 07:15 (62 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.
- Departs 07:0596 flights27.8%
- Departs 07:1070 flights20.3%
- Departs 07:1562 flights18.0%
Scale runs 0% to 100%. Rows with fewer than 30 flights show a dash.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 07:05 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and DL 1399 runs 4 points worse at 84.9%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.
Against the route
DL 1399 next to BOS to MIA
Every carrier on BOS to MIA combined arrived on time 77.7% of the time across 3,417 flights, so DL 1399 is 7 points ahead of it. Delta flew 890 flights on the same city pair under all its flight numbers, including this one, and those ran 72.1% on time. Across its whole network Delta Air Lines managed 81.6%, which this flight beats by 3 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 1399thin sample | 345 | 84.9% | 84 min | 2.03% | B |
| All Delta Air Lines on BOS–MIA | 890 | 72.1% | 76 min | 2.70% | C |
| All carriers on BOS–MIA | 3,417 | 77.7% | 75 min | 2.25% | B |
| Delta Air Lines, whole network | 1,038,570 | 81.6% | 71 min | 1.62% | B |
Across the year
DL 1399 quarter by quarter
DL 1399 did not run the same all year. Its best quarter was Jul–Sep 2025 at 92.2% on time and its weakest Jan–Mar 2026 at 80.8%, a swing of 11 points on roughly 86 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
- Jul–Sep 202592 flights92.2%
- Oct–Dec 202580 flights82.3%
- Jan–Mar 202682 flights80.8%
- Apr–Jun 202691 flights83.5%
Scale runs 70% to 100%. Rows with fewer than 30 flights show a dash.
By weekday, DL 1399 did best on Tuesday at 91.8% on time and worst on Thursday at 77.6%. Each day rests on about 49 flights, so a gap of 14 points is worth noticing but could still narrow in another year.
Delay causes
Why DL 1399 runs late
One category carries most of the weight here. Carrier accounts for 70% of the 4,282 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.
- 70%Carrier
- 23%National Airspace System
- 6%Late-arriving aircraft
- 1%Extreme weather
The largest share of delay minutes, 70%, 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 3,009 of the 4,282 delay minutes reported here. The split is drawn from 4,282 delay minutes reported on DL 1399.
Cancellations sit at 2.03% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
Badly late arrivals are rare here: only 4.1% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
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 same number turns up on two other city pairs in the data, including MIA to BOS (227) and SAT to DTW (9), but none flew often enough under DL 1399 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to BOS to MIA only.
One caution: this is a thin sample. 345 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 DL 1399
For a booking, read DL 1399 as 84.9% on time with 2.03% cancelled over 345 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- BOS to MIA, every carrier and departure
- MIA to BOS, the return direction
- Delta Air Lines 776 on the same route61.6%
- American Airlines 1259 on the same route87.9%
- American Airlines 2980 on the same route93.9%
- Boston Logan International (BOS) delay statistics
- Miami International (MIA) delay statistics
- Delta Air Lines on-time record
- Every Delta Air Lines flight number with a record
- The most and least reliable flight numbers in the US
- Worst months to fly in the US, ranked by the data
A flight number here means Delta Air Lines’s own number as it reports to the DOT. How the figures are computed is on the methodology page.
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.