Flight number record
DL 518
Delta Air Lines · Atlanta to Boston
- Route
- ATL → BOS
- Departs
- 16:20
- Flights
- 275
- Period
- July 2025 to June 2026
Historical statistics for July 2025 to June 2026, not live status. For today’s DL 518, check with Delta Air Lines.
DL 518 draws a D. Roughly one flight in two arrives at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 275 flights, with a median arrival 8 minutes late.
The national on-time rate over the same period is 77.6%, so DL 518 runs 19 points behind the country as a whole. Across a thousand flights that is about 195 extra late arrivals.
Key figures
On time
58.1%
Arrivals under 15 minutes late, of 272 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
1.09%
National rate is 1.81%
1 hour+ late
17.6%
National rate is 8.1%
These figures cover 275 flights between July 2025 and June 2026. Beyond the headline rate, 17.6% 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.
Schedule
When DL 518 flies
DL 518 flies ATL to BOS without a single fixed slot. Its most common scheduled departure was 16:20, used on 51 of 275 flights, with 16:25 (46 flights) and 16:30 (31 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.
- Departs 16:2051 flights18.5%
- Departs 16:2546 flights16.7%
- Departs 16:3031 flights11.3%
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 16:20 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 72.4%, and DL 518 runs 14 points worse at 58.1%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.
Against the route
DL 518 next to ATL to BOS
Every carrier on ATL to BOS combined arrived on time 74.5% of the time across 4,935 flights, so DL 518 is 16 points behind it. Delta flew 3,666 flights on the same city pair under all its flight numbers, including this one, and those ran 76.2% on time. Across its whole network Delta Air Lines managed 81.6%, which this flight trails by 23 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 518thin sample | 275 | 58.1% | 66 min | 1.09% | D |
| All Delta Air Lines on ATL–BOS | 3,666 | 76.2% | 59 min | 1.72% | B |
| All carriers on ATL–BOS | 4,935 | 74.5% | 63 min | 1.95% | C |
| Delta Air Lines, whole network | 1,038,570 | 81.6% | 71 min | 1.62% | B |
Across the year
DL 518 quarter by quarter
Quarter by quarter DL 518 held fairly steady: 55.7% in Jul–Sep 2025, 61.0% in Oct–Dec 2025, 57.5% in Jan–Mar 2026 and 57.9% in Apr–Jun 2026. A spread of 5 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.
- Jul–Sep 202579 flights55.7%
- Oct–Dec 202578 flights61.0%
- Jan–Mar 202641 flights57.5%
- Apr–Jun 202677 flights57.9%
Scale runs 45% to 65%. Rows with fewer than 30 flights show a dash.
By weekday, DL 518 did best on Wednesday at 71.1% on time and worst on Tuesday at 48.7%. Each day rests on about 39 flights, so a gap of 22 points is worth noticing but could still narrow in another year.
Delay causes
Why DL 518 runs late
One category carries most of the weight here. National Airspace System accounts for 53% of the 7,571 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.
- 53%National Airspace System
- 37%Carrier
- 7%Late-arriving aircraft
- 2%Extreme weather
- 1%Security
The largest share of delay minutes, 37%, 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 2,764 of the 7,571 delay minutes reported here. The split is drawn from 7,571 delay minutes reported on DL 518.
Cancellations sit at 1.09% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 17.6% 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 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. 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 MCO to BOS (12) and ECP to ATL (1), but none flew often enough under DL 518 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to ATL to BOS only.
One caution: this is a thin sample. 275 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 518
For a booking, DL 518 is a flight to put a long connection behind. 17.6% 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 route88.1%
- Delta Air Lines 865 on the same route79.8%
- Delta Air Lines 726 on the same route69.5%
- Delta Air Lines 350 on the same route75.5%
- Delta Air Lines 300 on the same route68.5%
- Delta Air Lines 987 on the same route89.8%
- 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.