Route reliability record
BWI→SEA
Baltimore to Seattle
- Flights
- 719
- Period
- September 2025 to August 2026
- Distance
- 2,335 mi
- Carriers
- 2
This route draws a C+. About one flight in three arrives at least 15 minutes late, and the typical late arrival is roughly 50 minutes behind schedule. Build slack into anything you connect to. That rests on 719 BWI to SEA flights, with a median arrival 2 minutes late.
Best time to fly BWI to SEA: a 8am–11am departure, ideally on a Tuesday. Flights in that window arrived on time 77.0% of the time and Tuesday flights 73.7%, against 66.8% for the route overall.
The national on-time rate over the same period is 77.3%, so this route runs 11 points behind the country as a whole. Across a thousand flights that is about 105 extra late arrivals.
Key figures
On time
66.8%
Arrivals under 15 minutes late, of 713 completed flights
Avg delay
52 min
Across delayed arrivals only, not all flights
Cancelled
0.83%
National rate is 1.89%
Best carrier
Alaska
68.2% on time across 599 flights
These figures cover 719 flights between September 2025 and August 2026. Beyond the headline rate, 8.4% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Which airline is most reliable on BWI to SEA
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Alaska Airlines | 599 | 68.2% | 49 min | 0.83% | C+ |
| Southwest Airlinesthin sample | 120 | 59.7% | 64 min | 0.83% | D+ |
Flight by flight
Flights on BWI to SEA
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 Baltimore to Seattle
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. 3 of the top 4 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. IAD → SEAWashington to Seattle | United Airlines | 80.9% | 81.3% | 0.48% | 8am–11am, Sat | UA 326 17:55 |
| 2. DCA → SEAWashington to Seattle | Alaska Airlines | 75.9% | 76.4% | 0.69% | 8am–11am, Sat | AS 1 08:00 |
| 3. IAD → SEAWashington to Seattle | Alaska Airlines | 74.5% | 75.4% | 1.20% | 8am–11am, Thu | — |
| 4. BWI → SEABaltimore to Seattle | Alaska Airlines | 67.6% | 68.2% | 0.83% | 8am–11am, Mon | AS 379 18:07 |
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 33 points, against half a point between the best and worst carrier.
- 5am–8am207 flights74.8%
- 8am–11am102 flights77.0%
- 11am–2pm17 flights—
- 2pm–5pm36 flights44.4%
- 5pm–8pm357 flights63.0%
- 8pm–5am—
Scale runs 35% to 80%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 77.0% of the time, against 44.4% for the afternoon window. That is 33 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 357 flights scheduled in it.
Explore
Filter BWI to SEA 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 BWI to SEA, the best departure window is 8am–11am at 77.0% on time and the worst is 2pm–5pm at 44.4%, a wide gap of 32.6 points. All US flights leaving 8am–11am ran 83.9%.
- 5–8am74.8%
- 8–11am77.0%
- 11am–2pm—
- 2–5pm44.4%
- 5–8pm63.0%
- 8pm–5am—
best all US flightsScale 35% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 57 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
December is the weak month at 32.2% on time, against 89.1% in October. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. August was the busiest month here, with 93 flights.
Across the week, Tuesday is the strongest day at 73.7% on time and Thursday the weakest at 57.1%, a spread of 17 points.
Delay causes
Why this route gets delayed
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 12,000 reported delay minutes.
- 39%National Airspace System
- 29%Late-arriving aircraft
- 16%Carrier
- 14%Extreme weather
- 2%Security
Extreme weather accounts for 14% of delay minutes, well above the single-digit share typical across the system. Weather delays are lumpy: they arrive as whole bad days rather than as a steady drag, so the monthly strip above is the more useful view of the risk. The national share is 6%, so this operation carries roughly 2.4 times the usual weather exposure. The split is drawn from 12,241 reported delay minutes.
39% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 4,783 minutes out of 12,000, against a national NAS share of 21%.
Cancellations are rare at 0.83%, 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
8.4% 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 roughly 50 minutes, which a normal layover absorbs.
At 2,335 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 80.7% on time across 719 flights, 14 points above 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 14 points of difference.
One caution: this is a thin sample. 719 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.
Work out the risk of missing a connection in SEA after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 719 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 66.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 713 completed flights over 12 months sit behind that.
Common questions
BWI to SEA questions
How often is BWI to SEA delayed?
About one flight in three arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 33.2% of the 719 flights in this analysis, against 22.7% nationally. Delayed flights are late by roughly 50 minutes on average.
How reliable is BWI to SEA compared with the rest of the country?
66.8% of flights arrive on time here against a national 77.3%, a difference of 11 points against it. That is worth a C+ on this site's grading scale.
What time of day has the fewest delays on BWI to SEA?
The 8am–11am departure window is the strongest at 77.0% on time. The 2pm–5pm window is the weakest at 44.4%, 33 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 December delays on BWI to SEA?
December is the weakest month at 32.2% on time, compared with 89.1% in October. Across the year that is 57 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
- SEA to BWI — the return legseparate record
- Baltimore/Washington International Thurgood Marshall (BWI) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Alaska Airlines on BWI to SEA68.2%
- Southwest Airlines on BWI to SEA59.7%
- BWI to ATL, a related route79.9%
- LAX to SEA, a related route85.0%
- BWI to MCO, a related route75.5%
- Alaska Airlines on-time record68.2%
- Southwest Airlines on-time record59.7%
- The best time of day to fly, according to 7.05 million flight records
- Connecting flights: how much buffer the data says you need
Direction matters. BWI to SEA and SEA to BWI 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.