Carrier route record
DLSEA→IAD
Delta Air Lines · Seattle to Washington
- Flights
- 361
- Period
- September 2025 to August 2026
- Share of route
- 20%
- Carriers
- 3
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on SEA to IAD lands a B, level with the national rate of 77.3%. About one flight in four arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That rests on 361 flights. The strongest carrier on the route with a full sample, United Airlines, flew 626 at 91.4% on time.
The US average over the same twelve months is 77.3%, so there is little to separate Delta on SEA to IAD from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
76.7%
Arrivals under 15 minutes late, of 356 completed flights
Avg delay
80 min
Across delayed arrivals only, not all flights
Cancelled
1.11%
National rate is 1.89%
Whole route
84.8%
Every carrier on SEA to IAD, 1,822 flights
These figures cover 361 flights between September 2025 and August 2026. Beyond the headline rate, 10.7% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Delta against every carrier on SEA to IAD
Delta flew 361 of the 1,822 flights on SEA to IAD, about 20% of it. Its 76.7% on time is 8 points worse than the route as a whole, which runs 84.8%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from United at 91.4% to Delta at 76.7%.
The choice of carrier is not cosmetic here. United Airlines arrives on time 91.4% of the time; Alaska Airlines manages 83.3%. Sample sizes sit next to every figure, because a two-point gap across 835 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 626 | 91.4% | 76 min | 0.64% | A+ |
| Alaska Airlines | 835 | 83.3% | 38 min | 0.36% | B+ |
| Delta Air Lines (this page)thin sample | 361 | 76.7% | 80 min | 1.11% | B |
United leads Alaska by 8 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Delta flight numbers on SEA to IAD
Timetable by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Departure window
When Delta runs best on this route
Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 361 flights.
- 5am–8am—
- 8am–11am—
- 11am–2pm—
- 2pm–5pm309 flights77.3%
- 5pm–8pm17 flights—
- 8pm–5am35 flights71.4%
Scale runs 65% to 85%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 2pm–5pm slot at 77.3% on time, ahead of 8pm–5am at 71.4%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 2pm–5pm window is the busiest, with 309 flights scheduled in it.
Across the year
Delta on SEA to IAD through the year
- Jul–Sep 202530 flights73.3%
- Oct–Dec 202589 flights77.3%
- Jan–Mar 202689 flights72.1%
- Apr–Jun 202691 flights83.3%
- Jul–Sep 202662 flights74.2%
Scale runs 65% to 90%.
Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 76.7% on time across 361 flights.
Delta on SEA to IAD did not run the same all year. Its best quarter was Apr–Jun 2026 at 83.3% on time and its weakest Jan–Mar 2026 at 72.1%, a swing of 11 points on roughly 72 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.
Across the week, Wednesday is the strongest day at 86.0% on time and Friday the weakest at 68.0%, a spread of 18 points.
Arrival by arrival
How late Delta on SEA to IAD runs when it is late
Delta on SEA to IAD often beats the schedule: 107 of 356 completed flights, 30%, arrived 15 minutes or more early. The 83 late arrivals split 23 under half an hour, 22 between 30 and 60 minutes, and 38 an hour or more.
- 15+ min early107 flights30.1%
- Within 15 min166 flights46.6%
- 15–29 min late23 flights6.5%
- 30–59 min late22 flights6.2%
- 1–2 hours late24 flights6.7%
- 2+ hours late14 flights3.9%
Scale runs 0% to 100%.
Share of 356 completed flights by arrival against schedule.
19 of 88 late departures made up the time and arrived on time, 22% of them. 14 flights left on time and still arrived late.
The worst days
Worst days for Delta on SEA to IAD
The latest arrival of the period was on 16 October 2025, 15 hours 3 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 |
|---|---|---|
| 16 October 2025 | 15 hours 3 minutes | Carrier |
| 21 August 2026 | 5 hours 3 minutes | Carrier |
| 15 December 2025 | 4 hours 51 minutes | Carrier |
| 27 January 2026 | 4 hours 7 minutes | Extreme weather |
| 22 July 2026 | 3 hours 13 minutes | Late-arriving aircraft |
Delay causes
Why Delta runs late on this route
Carrier accounts for 65% of the 6,629 delay minutes carriers reported here, and the remaining four split what is left.
- 65%Carrier
- 20%Late-arriving aircraft
- 9%National Airspace System
- 6%Extreme weather
The largest share of delay minutes, 65%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 4,316 of the 6,629 delay minutes reported here. The split is drawn from 6,629 reported delay minutes.
Cancellations sit at 1.11% against a national 1.89%, which is ordinary. Diversions add another 0.28%.
Connections and stage length
What a delay here costs
10.7% 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.
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 return leg runs 76.6% on time across 361 flights, within half a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
One caution: this is a thin sample. 361 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 Delta on SEA to IAD
Put together: treat all of this as provisional. 361 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 76.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 356 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to IAD, every carrier
- Delta on IAD to SEA, the return leg
- United Airlines on SEA to IAD91.4%
- Alaska Airlines on SEA to IAD83.3%
- Delta Air Lines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Washington Dulles International (IAD) delay statistics
- How often a connection fails at the major US hubs
- Connecting flights: how much buffer the data says you need
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.