Route profile
IAD→SEA
Flight reliability, delays and best times to fly from Washington to Seattle, 2,306 miles.
Right now
Aviation weather is not currently a factor.
Aviation weather is not currently a factor.
Route reliability
July 2023 – July 2026
Better than 60% of comparable major US routes (4,598 compared)
Calculated from 6,521 flights. How this is calculated · What counts as on time
IAD → SEA arrives on time 79.4% of the time; the return trip, SEA → IAD, arrives on time 81.3% of the time.
IAD → SEA spends 32.5 minutes on the ground on a 2,306-mile trip: 20.4 minutes from pushback to wheels-up at IAD and 12.0 minutes from touchdown to gate at SEA.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
What stands out
Every day of the week performs about the same on this route, steadier than 98% of 4,467 comparable routes.
81.1% on time on the best day (Wednesday) against 77.7% on the worst (Monday).
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Ranked against every other route with the same kind of figure and at least 4,467 in the comparison.
What sets this route apart
Where IAD to SEA differs most from similar routes by hour, weekday, month and airline, July 2023 – July 2026.
IAD to SEA is at its best against routes of similar length for flights scheduled at 1 PM: 90.3% arrive on time, 14.7 points ahead of the 75.6% those routes manage at that hour. Against all other routes the gap is 13.2 points.
IAD to SEA struggles most at 10 PM: 69.4% of its flights scheduled then arrive on time, 12.2 points behind the 81.6% on routes of similar length at the same hour.
October is kinder to IAD to SEA than to routes of similar length: 90.6% on time against 83.4%, 7.2 points better. Against all other routes the gap is 7.6 points.
In December, IAD to SEA runs 5.8 points below routes of similar length, 73.4% on time to 79.2%. Against all other routes the gap is 5.4 points.
Delta Air Lines’ flights on IAD to SEA arrive on time 78.8% of the time, 2.5 points below the 81.3% it manages on its routes of similar length. Against all other routes the gap is 2.7 points.
IAD to SEA against comparable routes
July 2023 – July 2026| Measure | This route | Compared with | Them | Gap | Flights behind it |
|---|---|---|---|---|---|
| Hour: 1 PM departures | 90.3% | routes of similar length | 75.6% | +14.7 pts | 206 here, 56,119 there |
| Hour: 10 PM departures | 69.4% | routes of similar length | 81.6% | −12.2 pts | 235 here, 67,206 there |
| Month: October | 90.6% | routes of similar length | 83.4% | +7.2 pts | 565 here, 93,994 there |
| Month: December | 73.4% | routes of similar length | 79.2% | −5.8 pts | 384 here, 90,761 there |
| Airline: Delta Air Lines | 78.8% | routes of similar length | 81.3% | −2.5 pts | 1,455 here, 233,638 there |
Each comparison pools the flights of other routes, with this route’s own left out. Similar length means within 15% of this route’s 2,306 miles, with at least 5 such routes. A bucket is set against the most comparable group that has enough flights: similar length, then the same origin (at least 3 routes), then all other routes. Hours, weekdays and months appear only where both sides have 120 completed flights, and airlines where both have 600. The gap must be at least 2 points and 2 standard errors, and only the largest gap each way is kept per measure. These are differences in the flights counted, not causes.
Why IAD → SEA flights are cancelled
July 2023 – July 2026
IAD → SEA cancelled 74 of 6,521 scheduled flights — about 1 in every 88. The reason filed most often was the airline, 78.4% of the cancellations coded on this route — about 1 in every 112 scheduled flights.
Share of cancellations
Of 74 cancelled departures carrying a reason code.
What each reason means
Crew, maintenance, aircraft cleaning, baggage or fueling: what BTS counts as within the carrier’s own control.
58 cancellations, 78.4% of the total.
Conditions the carrier judged severe enough to stop the flight: a blizzard, a hurricane, a line of thunderstorms.
16 cancellations, 21.6% of the total.
Airport capacity, air traffic control flow programs, heavy traffic and ordinary bad weather. A system decision, not the airline’s.
0 cancellations, 0.0% of the total.
A terminal evacuation, a security breach, screening equipment failure, or screening queues over 29 minutes.
0 cancellations, 0.0% of the total.
Reason codes are the operating airline’s own filing with US DOT, not an independent finding of fault. Ordinary bad weather is filed under air traffic, so weather’s full share is larger than its bar.
74 coded cancellations were recorded on IAD → SEA; the section appears from 50.
When it goes wrong
July 2023 – July 2026
37 min late
against a median of 7 min early
Percentiles over 6,521 operations; cancelled and diverted flights are counted separately.
Will your connection be tight enough?
Layovers at SEA after arriving from IAD.
| Connection time | Chance of missing | Reads as |
|---|---|---|
| 30 min | 36% | Likely to miss |
| 45 min | 20% | High risk |
| 60 min | 12% | Some risk |
| 90 min | 6.2% | Some risk |
| 120 min | 3.9% | Low risk |
This is one leg of a connection. Gate changes and the next flight's own schedule matter too. And a connection can fail before delay is even the question — this route cancels 1.13% of the time and diverts 0.25% of the time, which a late arrival never shows up in.
Chance of missing is the share of 6,431 arrivals on this route that landed later than the connection time less 30 minutes to reach the next gate.
The worst tenth of arrivals on this route land at least 37 minutes late (90th-percentile gate arrival delay), over 6,521 operations.
Any other layover length: connection checker.
Best time to fly
IAD → SEA flights departing 12–3 PM arrived on time 90.6% of the time, against 68.1% for 6–9 PM departures, a gap of 22.5 percentage points.
By departure window
By departure hour
- 12 AM to 5 AM: too few flights to score
- 6 AM: 94.0% on time from 218 flights
- 7 AM: 82.1% on time from 1,668 flights
- 8 AM: 91.3% on time from 548 flights
- 9 AM: 81.4% on time from 452 flights
- 10 AM to 11 AM: too few flights to score
- 12 PM: 90.9% on time from 209 flights
- 1 PM: 90.3% on time from 206 flights
- 2 PM to 3 PM: too few flights to score
- 4 PM: 82.1% on time from 159 flights
- 5 PM: 74.7% on time from 1,696 flights
- 6 PM: 64.8% on time from 609 flights
- 7 PM: 72.9% on time from 418 flights
- 8 PM to 9 PM: too few flights to score
- 10 PM: 69.4% on time from 239 flights
- 11 PM: too few flights to score
Why IAD → SEA runs late
July 2023 – July 2026
crew, maintenance, boarding and fueling, all within the carrier’s control
the inbound aircraft was late, so this flight started late
airspace and airport capacity, including weather-driven flow control
weather severe enough to stop this flight specifically
screening or terminal security incidents
Share of the delay minutes US DOT attributed to each cause for IAD → SEA. Only delays of 15 minutes or more are attributed. What the five causes mean
Airlines on this route
Carriers with at least 200 flights, by the airline that operated each one.
| Carrier | Flights | On time | Cancelled | Median delay | Severe |
|---|---|---|---|---|---|
| Alaska Airlines | 2,625 | 77.5% | 0.99% | -6 min | 6.1% |
| United Airlines | 2,421 | 81.8% | 1.40% | -9 min | 5.8% |
| Delta Air Lines | 1,475 | 78.8% | 0.95% | -8 min | 7.6% |
Alaska Airlines flew 40.3% of the 6,521 flights listed.
United Airlines arrived on time 4.3 percentage points more often than Alaska Airlines on this route.
Flights on this route
Flight numbers with at least 600 operations here and still on the schedule.
Weekly and seasonal patterns
By day of week
Wednesday is historically the most reliable day and Monday the least, a gap of 3.4 percentage points.
By month
- Jan: 79.6%
- Feb: 78.3%
- Mar: 74.6%
- Apr: 82.2%
- May: 79.7%
- Jun: 71.1%
- Jul: 74.7%
- Aug: 79.2%
- Sep: 88.0%
- Oct: 90.6%
- Nov: 82.3%
- Dec: 73.4%
June is historically the weakest month and October the strongest, a spread of 19.5 percentage points.
Reliability over time
July 2023 – July 2026
- July 2023: 62.5% from 257 flights
- August 2023: 77.7% from 279 flights
- September 2023: 84.6% from 242 flights
- October 2023: 93.6% from 220 flights
- November 2023: 76.6% from 145 flights
- December 2023: 86.8% from 129 flights
- January 2024: too few flights to score (105)
- February 2024: too few flights to score (95)
- March 2024: too few flights to score (118)
- April 2024: 78.8% from 146 flights
- May 2024: 70.4% from 226 flights
- June 2024: 65.2% from 270 flights
- July 2024: 81.0% from 278 flights
- August 2024: 79.7% from 265 flights
- September 2024: 88.1% from 230 flights
- October 2024: 92.2% from 193 flights
- November 2024: 95.6% from 181 flights
- December 2024: 83.5% from 135 flights
- January 2025: too few flights to score (104)
- February 2025: too few flights to score (93)
- March 2025: too few flights to score (116)
- April 2025: 85.2% from 155 flights
- May 2025: 83.7% from 203 flights
- June 2025: 71.6% from 240 flights
- July 2025: 73.6% from 245 flights
- August 2025: 80.5% from 221 flights
- September 2025: 92.2% from 179 flights
- October 2025: 84.4% from 156 flights
- November 2025: too few flights to score (119)
- December 2025: 48.4% from 124 flights
- January 2026: too few flights to score (103)
- February 2026: too few flights to score (93)
- March 2026: too few flights to score (117)
- April 2026: 82.7% from 128 flights
- May 2026: 86.1% from 201 flights
- June 2026: 78.5% from 198 flights
- July 2026: 82.8% from 212 flights
Over the most recent 12 months (2025-08 to 2026-07), on-time arrivals averaged 77.6% against 81.9% in the 12 months before — declining by 4.3 percentage points.
Data and methodology
Calculated by FlyerIntel from 6,521 IAD → SEA flight records from the US DOT Bureau of Transportation Statistics, covering July 2023 – July 2026. Late means 15 or more minutes past scheduled arrival; cancelled and diverted flights are left out of on-time rates.
Full methodology · Data sources · Report a problem
Related research: How Long a Layover Needs to Be · Two Airlines on One Route · Best Time of Day to Fly From Major US Airports
Analysis last recomputed