Flight number record
DL 1399
Delta Air Lines · Boston to Miami
- Route
- BOS → MIA
- Departs
- 07:05
- Flights
- 345
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 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 77.3%. 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 77.3%. That gap is worth roughly 67 fewer late arrivals for every thousand flights.
Key figures
On time
84.0%
Arrivals under 15 minutes late, of 338 completed flights
Avg delay
90 min
Across delayed arrivals only, not all flights
Cancelled
2.03%
National rate is 1.89%
1 hour+ late
5.0%
National rate is 8.3%
These figures cover 345 flights between September 2025 and August 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.
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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 118 of 345 flights, with 07:10 (70 flights) and 07:20 (55 flights) next.
- Departs 07:05118 flights34.2%
- Departs 07:1070 flights20.3%
- Departs 07:2055 flights15.9%
Scale runs 0% to 100%.
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 5 points worse at 84.0%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.
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Against the route
DL 1399 next to BOS to MIA
Every carrier on BOS to MIA combined arrived on time 78.0% of the time across 3,368 flights, so DL 1399 is 6 points ahead of it. Delta flew 892 flights on the same city pair under all its flight numbers, including this one, and those ran 72.4% on time. Across its whole network Delta Air Lines managed 81.1%, which this flight beats by 3 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 1399thin sample | 345 | 84.0% | 90 min | 2.03% | B |
| All Delta Air Lines on BOS–MIA | 892 | 72.4% | 78 min | 2.58% | C |
| All carriers on BOS–MIA | 3,368 | 78.0% | 78 min | 2.17% | B |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 1399 quarter by quarter
Quarter by quarter DL 1399 held fairly steady: 90.0% in Jul–Sep 2025, 82.3% in Oct–Dec 2025, 80.8% in Jan–Mar 2026, 83.5% in Apr–Jun 2026 and 88.3% in Jul–Sep 2026. A spread of 9 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.
- Jul–Sep 202530 flights90.0%
- Oct–Dec 202580 flights82.3%
- Jan–Mar 202682 flights80.8%
- Apr–Jun 202691 flights83.5%
- Jul–Sep 202662 flights88.3%
Scale runs 70% to 95%.
By weekday, DL 1399 did best on Wednesday at 89.8% on time and worst on Thursday at 76.0%. Each day rests on about 49 flights, so a gap of 14 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late DL 1399 runs when it is late
DL 1399 often beats the schedule: 112 of 338 completed flights, 33%, arrived 15 minutes or more early. The 54 late arrivals split 20 under half an hour, 17 between 30 and 60 minutes, and 17 an hour or more.
- 15+ min early112 flights33.1%
- Within 15 min172 flights50.9%
- 15–29 min late20 flights5.9%
- 30–59 min late17 flights5.0%
- 1–2 hours late5 flights1.5%
- 2+ hours late12 flights3.6%
Scale runs 0% to 100%.
Share of 338 completed flights by arrival against schedule.
Time lost at the gate mostly stays lost. Of 36 departures that left 15 minutes late or more, only 3 made it up before arrival. In the other direction, 21 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at MIA.
The worst days
Worst days for DL 1399
The latest arrival of the period was on 3 May 2026, 13 hours 50 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on five of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 3 May 2026 | 13 hours 50 minutes | Carrier |
| 19 January 2026 | 6 hours 24 minutes | Carrier |
| 6 July 2026 | 5 hours 35 minutes | Carrier |
| 31 March 2026 | 5 hours 5 minutes | Carrier |
| 14 November 2025 | 4 hours 16 minutes | Carrier |
Delay causes
Why DL 1399 runs late
Carrier accounts for 75% of the 4,871 delay minutes carriers reported here, and the remaining four split what is left.
- 75%Carrier
- 19%National Airspace System
- 5%Late-arriving aircraft
- 1%Extreme weather
The largest share of delay minutes, 75%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 3,671 of the 4,871 delay minutes reported here. The split is drawn from 4,871 delay minutes reported on DL 1399.
Cancellations sit at 2.03% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
5.0% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last an hour and a half, 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.
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 84.0% 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 route63.1%
- American Airlines 1259 on the same route88.6%
- American Airlines 2980 on the same route92.7%
- 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
- How to read this site: grades, sample sizes, and honest caveats
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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.