Flight number record

DL 2639

Delta Air Lines · New York to Boston

Route: JFK → BOS
Departs: 21:00
Flights: 349
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s DL 2639, check with Delta Air Lines.

DL 2639 sits in the middle of the pack with a C−. About seven flights in ten arrive on time by the DOT's definition, 9 points worse than the national rate of 77.6%. The late ones land an hour and a half behind schedule. That rests on 349 flights, with a median arrival 5 minutes early.

The national on-time rate over the same period is 77.6%, so DL 2639 runs 9 points behind the country as a whole. Across a thousand flights that is about 94 extra late arrivals.

On time

68.2%

Arrivals under 15 minutes late, of 337 completed flights

Avg delay

93 min

Across delayed arrivals only, not all flights

Cancelled

3.44%

National rate is 1.81%

1 hour+ late

16.3%

National rate is 8.1%

These figures cover 349 flights between July 2025 and June 2026. Beyond the headline rate, 16.3% 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 2639 flies

DL 2639 flies JFK to BOS without a single fixed slot. Its most common scheduled departure was 21:00, used on 95 of 349 flights, with 20:59 (56 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 21:0095 flights27.2%
Departs 20:5956 flights16.0%

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 21:00 departure sits in the 8pm–5am window. Across every US flight scheduled in that window the on-time rate is 70.5%, and DL 2639 runs 2 points worse at 68.2%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.

Against the route

DL 2639 next to JFK to BOS

Every carrier on JFK to BOS combined arrived on time 73.7% of the time across 5,744 flights, so DL 2639 is 6 points behind it. Across its whole network Delta Air Lines managed 81.6%, which this flight trails by 13 points.

DL 2639 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 2639thin sample	349	68.2%	93 min	3.44%	C−
All Delta Air Lines on JFK–BOS	368	68.8%	93 min	3.26%	C−
All carriers on JFK–BOS	5,744	73.7%	78 min	4.18%	C−
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	B

Across the year

DL 2639 quarter by quarter

DL 2639 did not run the same all year. Its best quarter was Jan–Mar 2026 at 76.2% on time and its weakest Jul–Sep 2025 at 61.8%, a swing of 14 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 202592 flights61.8%
Oct–Dec 202580 flights65.8%
Jan–Mar 202686 flights76.2%
Apr–Jun 202691 flights69.7%

Scale runs 55% to 80%. Rows with fewer than 30 flights show a dash.

By weekday, DL 2639 did best on Friday at 74.0% on time and worst on Thursday at 55.3%. Each day rests on about 50 flights, so a gap of 19 points is worth noticing but could still narrow in another year.

Delay causes

Why DL 2639 runs late

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 9,956 reported delay minutes.

Late-arriving aircraft
42%
Carrier
40%
National Airspace System
18%
Extreme weather
0%

42% 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 9,956 reported delay minutes here, that single category outweighs weather by 42 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 9,956 delay minutes reported on DL 2639.

Cancellations run at 3.44%, against 1.81% nationally. That is about 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 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. 16.3% 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.

Every one of the 349 flights under DL 2639 in the data flew JFK 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 2639

For a booking, the cancellation rate is the figure to plan around on DL 2639: 3.44% of its 349 scheduled flights did not operate. A late arrival costs an hour and a half, but a cancellation costs the day, so leave a later option open.

Where to go next

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.

Key figures