Flight number record
DL 821
Delta Air Lines · Atlanta to Boston
- Route
- ATL → BOS
- Departs
- 18:15
- Flights
- 349
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s DL 821, check with Delta Air Lines.
DL 821 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 77.3%. The late ones land about an hour behind schedule. That rests on 349 flights, with a median arrival 2 minutes late.
The national on-time rate over the same period is 77.3%, so DL 821 runs 8 points behind the country as a whole. Across a thousand flights that is about 81 extra late arrivals.
Key figures
On time
69.2%
Arrivals under 15 minutes late, of 344 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
1.43%
National rate is 1.89%
1 hour+ late
12.5%
National rate is 8.3%
These figures cover 349 flights between September 2025 and August 2026. Beyond the headline rate, 12.5% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Schedule
When DL 821 flies
DL 821 flies ATL to BOS without a single fixed slot. Its most common scheduled departure was 18:15, used on 71 of 349 flights, with 17:55 (56 flights) and 18:25 (46 flights) next.
- Departs 18:1571 flights20.3%
- Departs 17:5556 flights16.0%
- Departs 18:2546 flights13.2%
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 18:15 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.0%, and DL 821 runs level with that at 69.2%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.
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Against the route
DL 821 next to ATL to BOS
Every carrier on ATL to BOS combined arrived on time 72.8% of the time across 5,054 flights, so DL 821 is 4 points behind it. Delta flew 3,731 flights on the same city pair under all its flight numbers, including this one, and those ran 74.4% on time. Across its whole network Delta Air Lines managed 81.1%, which this flight trails by 12 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 821thin sample | 349 | 69.2% | 66 min | 1.43% | C |
| All Delta Air Lines on ATL–BOS | 3,731 | 74.4% | 61 min | 1.82% | C |
| All carriers on ATL–BOS | 5,054 | 72.8% | 66 min | 2.30% | C |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 821 quarter by quarter
DL 821 did not run the same all year. Its best quarter was Jan–Mar 2026 at 76.7% on time and its weakest Jul–Sep 2026 at 60.3%, a swing of 16 points on roughly 87 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 202520 flights—
- Oct–Dec 202591 flights67.4%
- Jan–Mar 202689 flights76.7%
- Apr–Jun 202691 flights70.3%
- Jul–Sep 202658 flights60.3%
Scale runs 50% to 80%. Rows with fewer than 30 flights show a dash.
By weekday, DL 821 did best on Friday at 76.5% on time and worst on Sunday at 61.4%. Each day rests on about 50 flights, so a gap of 15 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late DL 821 runs when it is late
The 106 late arrivals split 29 under half an hour, 34 between 30 and 60 minutes, and 43 an hour or more.
- 15+ min early54 flights15.7%
- Within 15 min184 flights53.5%
- 15–29 min late29 flights8.4%
- 30–59 min late34 flights9.9%
- 1–2 hours late28 flights8.1%
- 2+ hours late15 flights4.4%
Scale runs 0% to 100%.
Share of 344 completed flights by arrival against schedule.
25 of 116 late departures made up the time and arrived on time, 22% of them. 15 flights left on time and still arrived late.
The worst days
Worst days for DL 821
The latest arrival of the period was on 7 December 2025, 5 hours 54 minutes behind schedule; most of its delay minutes were filed as extreme weather. On three of the five worst days the largest share was filed as national airspace system delay.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 7 December 2025 | 5 hours 54 minutes | Extreme weather |
| 6 November 2025 | 4 hours | National Airspace System |
| 18 July 2026 | 3 hours 26 minutes | Carrier |
| 18 June 2026 | 3 hours 3 minutes | National Airspace System |
| 7 July 2026 | 3 hours 2 minutes | National Airspace System |
Delay causes
Why DL 821 runs late
National Airspace System accounts for 48% of the 6,940 delay minutes carriers reported here, and the remaining four split what is left.
- 48%National Airspace System
- 32%Carrier
- 14%Late-arriving aircraft
- 6%Extreme weather
48% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 3,347 minutes out of 6,940, against a national NAS share of 21%. The split is drawn from 6,940 delay minutes reported on DL 821.
Cancellations sit at 1.43% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
12.5% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection here, and two hours if the onward flight is on a separate ticket.
The 946 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.
Every one of the 349 flights under DL 821 in the data flew ATL to BOS. The number was not reused on any other city pair, which makes this a clean record of one route.
One caution: this is a thin sample. 349 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 821
For a booking, DL 821 is a flight to put a long connection behind. 12.5% of its completed flights arrived an hour or more late, which a short layover will not absorb. If the onward flight is on a separate ticket, the risk sits with you.
Related
Where to go next
- ATL to BOS, every carrier and departure
- BOS to ATL, the return direction
- Delta Air Lines 855 on the same route85.2%
- Delta Air Lines 865 on the same route80.2%
- Delta Air Lines 726 on the same route66.3%
- Delta Air Lines 987 on the same route89.9%
- Delta Air Lines 350 on the same route74.6%
- Delta Air Lines 2595 on the same route62.5%
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Boston Logan International (BOS) 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 often a connection fails at the major US hubs
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.