Flight number record
DL 1015
Delta Air Lines · Washington to Seattle
- Route
- IAD → SEA
- Departs
- 07:00
- Flights
- 349
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 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 77.3%. 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 rests on 349 flights, with a median arrival 5 minutes early.
Key figures
On time
77.0%
Arrivals under 15 minutes late, of 344 completed flights
Avg delay
91 min
Across delayed arrivals only, not all flights
Cancelled
1.15%
National rate is 1.89%
1 hour+ late
7.8%
National rate is 8.3%
These figures cover 349 flights between September 2025 and August 2026. The median arrival is 5 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 1015 flies
DL 1015 flies IAD to SEA without a single fixed slot. Its most common scheduled departure was 07:00, used on 148 of 349 flights, with 07:35 (69 flights) and 07:30 (62 flights) next.
- Departs 07:00148 flights42.4%
- Departs 07:3569 flights19.8%
- Departs 07:3062 flights17.8%
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 07:00 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 77.0%. 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 1015 next to IAD to SEA
Every carrier on IAD to SEA combined arrived on time 77.7% of the time across 1,821 flights, so DL 1015 is about level with it. Across its whole network Delta Air Lines managed 81.1%, which this flight trails by 4 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 1015thin sample | 349 | 77.0% | 91 min | 1.15% | B |
| All Delta Air Lines on IAD–SEAthin sample | 361 | 76.6% | 88 min | 1.39% | B |
| All carriers on IAD–SEA | 1,821 | 77.7% | 64 min | 0.99% | B+ |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | 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 90.0% on time and its weakest Jan–Mar 2026 at 62.2%, a swing of 28 points on roughly 70 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 202530 flights90.0%
- Oct–Dec 202580 flights70.0%
- Jan–Mar 202686 flights62.2%
- Apr–Jun 202691 flights86.7%
- Jul–Sep 202662 flights85.5%
Scale runs 55% to 95%.
By weekday, DL 1015 did best on Monday at 86.0% on time and worst on Thursday at 70.0%. Each day rests on about 50 flights, so a gap of 16 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late DL 1015 runs when it is late
DL 1015 often beats the schedule: 110 of 344 completed flights, 32%, arrived 15 minutes or more early. The 79 late arrivals split 30 under half an hour, 22 between 30 and 60 minutes, and 27 an hour or more.
- 15+ min early110 flights32.0%
- Within 15 min155 flights45.1%
- 15–29 min late30 flights8.7%
- 30–59 min late22 flights6.4%
- 1–2 hours late10 flights2.9%
- 2+ hours late17 flights4.9%
Scale runs 0% to 100%.
Share of 344 completed flights by arrival against schedule.
9 of 51 late departures made up the time and arrived on time, 18% of them. In the other direction, 37 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 SEA.
The worst days
Worst days for DL 1015
The latest arrival of the period was on 13 November 2025, 11 hours 42 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 13 November 2025 | 11 hours 42 minutes | Carrier |
| 26 January 2026 | 8 hours 30 minutes | Extreme weather |
| 19 March 2026 | 8 hours 25 minutes | Carrier |
| 4 July 2026 | 7 hours 10 minutes | Carrier |
| 13 August 2026 | 6 hours 17 minutes | Late-arriving aircraft |
Delay causes
Why DL 1015 runs late
Carrier accounts for 64% of the 7,166 delay minutes carriers reported here, and the remaining four split what is left.
- 64%Carrier
- 23%National Airspace System
- 7%Extreme weather
- 6%Late-arriving aircraft
The largest share of delay minutes, 64%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 4,595 of the 7,166 delay minutes reported here. The split is drawn from 7,166 delay minutes reported on DL 1015.
Cancellations sit at 1.15% against a national 1.89%, which is ordinary. Diversions add another 0.29%.
Connections and routes
What a delay on this flight costs
7.8% 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.
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 77.0% on time with 1.15% cancelled over 349 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- IAD to SEA, every carrier and departure
- SEA to IAD, the return direction
- United Airlines 326 on the same route76.2%
- Washington Dulles International (IAD) delay statistics
- Seattle-Tacoma International (SEA) 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
- Worst months to fly in the US, ranked by the data
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.