Route reliability record
SEA→IAD
Seattle to Washington
- Flights
- 1,822
- Period
- September 2025 to August 2026
- Distance
- 2,305 mi
- Carriers
- 3
This route earns a B+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 8 points better than the national rate of 77.3%. When something does go wrong the average delay runs about an hour. That rests on 1,822 SEA to IAD flights, of which United Airlines flew 626 at 91.4% on time.
Best time to fly SEA to IAD: a 11am–2pm departure, ideally on a Wednesday. Flights in that window arrived on time 90.4% of the time and Wednesday flights 91.5%, against 84.8% for the route overall.
Set against the rest of the country, this route's record is 8 points better than the US average of 77.3%. That gap is worth roughly 75 fewer late arrivals for every thousand flights.
Key figures
On time
84.8%
Arrivals under 15 minutes late, of 1,802 completed flights
Avg delay
58 min
Across delayed arrivals only, not all flights
Cancelled
0.60%
National rate is 1.89%
Best carrier
United
91.4% on time across 626 flights
These figures cover 1,822 flights between September 2025 and August 2026. The median arrival is 11 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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Carrier by carrier
Which airline is most reliable on SEA to IAD
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 Linesthin 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
Flights on SEA to IAD
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly Seattle to Washington
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 2 of the top 4 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SEA → IADSeattle to Washington | United Airlines | 90.8% | 91.4% | 0.64% | 8am–11am, Tue | — |
| 2. SEA → BWISeattle to Baltimore | Alaska Airlines | 84.2% | 84.8% | 0.67% | 8pm–5am, Sat | AS 378 09:03 |
| 3. SEA → IADSeattle to Washington | Alaska Airlines | 83.0% | 83.3% | 0.36% | 8am–11am, Wed | AS 367 22:43 |
| 4. SEA → DCASeattle to Washington | Alaska Airlines | 77.5% | 78.0% | 0.69% | 8am–11am, Sat | AS 4 08:00 |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 11 points, against 8 points between the best and worst carrier.
- 5am–8am—
- 8am–11am726 flights88.4%
- 11am–2pm126 flights90.4%
- 2pm–5pm495 flights79.6%
- 5pm–8pm17 flights—
- 8pm–5am458 flights83.5%
Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 90.4% on time, ahead of 2pm–5pm at 79.6%. 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 8am–11am window is the busiest, with 726 flights scheduled in it.
Explore
Filter SEA to IAD by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On SEA to IAD, the best departure window is 11am–2pm at 90.4% on time and the worst is 2pm–5pm at 79.6%, a wide gap of 10.8 points. All US flights leaving 11am–2pm ran 78.3%.
- 5–8am—
- 8–11am88.4%
- 11am–2pm90.4%
- 2–5pm79.6%
- 5–8pm—
- 8pm–5am83.5%
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
Twelve months, one bar each, drawn from the same 1,822 flights. The strip shows how much of this route's record is set by the calendar rather than by the operation.
July is the worst month at 80.5% on time, 9 points below April, the best at 89.0%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. July was the busiest month here, with 212 flights.
Across the week, Wednesday is the strongest day at 91.5% on time and Monday the weakest at 82.7%, a spread of 9 points.
Delay causes
Why this route gets delayed
Carrier accounts for 53% of the 16,000 delay minutes carriers reported here, and the remaining four split what is left.
- 53%Carrier
- 28%Late-arriving aircraft
- 15%National Airspace System
- 4%Extreme weather
- 0%Security
The largest share of delay minutes, 53%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 8,435 of the 16,000 delay minutes reported here. The split is drawn from 15,856 reported delay minutes.
Cancellations are rare at 0.60%, below the national 1.89% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.2% land an hour or more behind schedule, against 8.3% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
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 is a different operation and performs like one: it runs 77.7% on time across 1,821 flights, 7 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 7 points of difference.
The sample behind these figures is 1,822 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in IAD after this flight
What to do with this
Booking this route
Put together: this route's record is 84.8% on time with 0.60% cancelled, worth a B+. The largest single lever is the 11am–2pm departure window, and the numbers below the table are where the reasoning behind that lives. 1,802 completed flights over 12 months sit behind that.
Common questions
SEA to IAD questions
How often is SEA to IAD delayed?
About one flight in seven arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 15.2% of the 1,822 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SEA to IAD?
United Airlines leads at 91.4% on time across 626 flights. Alaska Airlines is at the other end on 83.3%, a gap of 8 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on SEA to IAD?
The 11am–2pm departure window is the strongest at 90.4% on time. The 2pm–5pm window is the weakest at 79.6%, 11 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are July delays on SEA to IAD?
July is the weakest month at 80.5% on time, compared with 89.0% in April. Across the year that is 9 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- IAD to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- Washington Dulles International (IAD) delay statistics
- United Airlines on SEA to IAD91.4%
- Alaska Airlines on SEA to IAD83.3%
- Delta Air Lines on SEA to IAD76.7%
- SEA to LAX, a related route82.0%
- ATL to IAD, a related route76.4%
- SEA to PHX, a related route78.2%
- United Airlines on-time record91.4%
- Alaska Airlines on-time record83.3%
- Delta Air Lines on-time record76.7%
- The best time of day to fly, according to 7.05 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. SEA to IAD and IAD to SEA are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.