Flight number record

DL 1015

Delta Air Lines · Washington to Seattle

Route: IAD → SEA
Departs: 07:00
Flights: 349
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s DL 1015, check with Delta Air Lines.

DL 1015 lands a B, level with the national rate of 77.6%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 349 flights, with a median arrival 7 minutes early.

On time

77.6%

Arrivals under 15 minutes late, of 344 completed flights

Avg delay

96 min

Across delayed arrivals only, not all flights

Cancelled

1.15%

National rate is 1.81%

1 hour+ late

7.6%

National rate is 8.1%

These figures cover 349 flights between July 2025 and June 2026. The median arrival is 7 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 1015 flies

DL 1015 flies IAD to SEA without a single fixed slot. Its most common scheduled departure was 07:00, used on 115 of 349 flights, with 07:30 (97 flights) and 07:35 (90 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 07:00115 flights33.0%
Departs 07:3097 flights27.8%
Departs 07:3590 flights25.8%

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 07:00 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and DL 1015 runs 12 points worse at 77.6%. 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 1015 next to IAD to SEA

Every carrier on IAD to SEA combined arrived on time 76.6% of the time across 1,884 flights, so DL 1015 is about level with it. Across its whole network Delta Air Lines managed 81.6%, which this flight trails by 4 points.

DL 1015 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 1015thin sample	349	77.6%	96 min	1.15%	B
All Delta Air Lines on IAD–SEAthin sample	361	77.2%	93 min	1.39%	B
All carriers on IAD–SEA	1,884	76.6%	63 min	1.01%	B
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	B

Across the year

DL 1015 quarter by quarter

DL 1015 did not run the same all year. Its best quarter was Jul–Sep 2025 at 89.1% on time and its weakest Jan–Mar 2026 at 62.2%, a swing of 27 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 flights89.1%
Oct–Dec 202580 flights70.0%
Jan–Mar 202686 flights62.2%
Apr–Jun 202691 flights86.7%

Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.

By weekday, DL 1015 did best on Monday at 89.8% on time and worst on Thursday at 68.0%. Each day rests on about 50 flights, so a gap of 22 points is worth noticing but could still narrow in another year.

Delay causes

Why DL 1015 runs late

One category carries most of the weight here. Carrier accounts for 70% of the 7,357 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.

Carrier
70%
National Airspace System
22%
Extreme weather
7%
Late-arriving aircraft
1%

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 5,176 of the 7,357 delay minutes reported here. The split is drawn from 7,357 delay minutes reported on DL 1015.

Cancellations sit at 1.15% against a national 1.81%, which is ordinary. Diversions add another 0.29%.

Connections and routes

What a delay on this flight costs

7.6% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says 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.

At 2,305 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The same number turns up on one other city pair in the data, including DTW to FLL (16), but none flew often enough under DL 1015 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to IAD to SEA only.

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 1015

For a booking, read DL 1015 as 77.6% on time with 1.15% cancelled over 349 flights. Those are rates from the past twelve months, not a forecast for any particular day.

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