Route reliability record
SEA→BWI
Seattle to Baltimore
- Flights
- 719
- Period
- July 2025 to June 2026
- Distance
- 2,335 mi
- Carriers
- 2
This route lands a B+, 3 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 40 minutes on average. That is a workable record, not a spotless one. That rests on 719 SEA to BWI flights, with a median arrival 6 minutes early.
The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
80.4%
Arrivals under 15 minutes late, of 713 completed flights
Avg delay
42 min
Across delayed arrivals only, not all flights
Cancelled
0.42%
National rate is 1.81%
Best carrier
Alaska
82.8% on time across 599 flights
These figures cover 719 flights between July 2025 and June 2026. The median arrival is 6 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.
Carrier by carrier
Which airline is most reliable on SEA to BWI
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 | 82.8% | 43 min | 0.50% | B+ |
| Southwest Airlinesthin sample | 120 | 68.3% | 41 min | 0.00% | C+ |
Flight by flight
Flights on SEA to BWI
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.
Best ways to make this trip
The most reliable ways to fly Seattle to Baltimore
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. 4 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SEA → DCASeattle to Washington | Delta Air Lines | 89.3% | 92.1% | 3.01% | 5am–8am, Sat | DL 786 07:20 |
| 2. SEA → IADSeattle to Washington | United Airlines | 85.9% | 86.5% | 0.72% | 8am–11am, Tue | — |
| 3. SEA → BWISeattle to Baltimore | Alaska Airlines | 82.4% | 82.8% | 0.50% | 8pm–5am, Sat | AS 378 10:11 |
| 4. SEA → IADSeattle to Washington | Alaska Airlines | 80.1% | 80.4% | 0.36% | 8pm–5am, Wed | AS 367 23:30 |
| 5. SEA → DCASeattle to Washington | Alaska Airlines | 75.6% | 76.4% | 1.10% | 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 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 719 flights.
- 5am–8am—
- 8am–11am365 flights82.5%
- 11am–2pm—
- 2pm–5pm—
- 5pm–8pm—
- 8pm–5am354 flights78.2%
Scale runs 70% to 90%. Rows with fewer than 30 flights show a dash.
The early departures do better, though not dramatically: 82.5% on time for the 8am–11am window against 78.2% for 8pm–5am. Worth taking if the schedule allows, not worth an extra connection. The 8am–11am window is the busiest, with 365 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 28 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.
August is the worst month at 66.7% on time, 28 points below April, the best at 94.7%. 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. August was the busiest month here, with 93 flights.
Across the week, Saturday is the strongest day at 86.2% on time and Sunday the weakest at 73.1%. 13 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Carrier accounts for 42% of the 5,927 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 42%Carrier
- 34%Late-arriving aircraft
- 20%National Airspace System
- 4%Extreme weather
- 0%Security
The largest share of delay minutes, 42%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 2,518 of the 5,927 delay minutes reported here. The split is drawn from 5,927 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 82.5% on time here.
Cancellations are rare at 0.42%, below the national 1.81% 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 3.5% land an hour or more behind schedule, against 8.1% 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 2,335 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 68.4% on time across 719 flights, 12 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 12 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 BWI 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 80.4% 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
SEA to BWI questions
How often is SEA to BWI delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 19.6% of the 719 flights in this analysis, against 22.4% nationally. Delayed flights are late by roughly 40 minutes on average.
How reliable is SEA to BWI compared with the rest of the country?
80.4% of flights arrive on time here against a national 77.6%, a difference of 3 points in its favour. That is worth a B+ on this site's grading scale.
What time of day has the fewest delays on SEA to BWI?
The 8am–11am departure window is the strongest at 82.5% on time. The 8pm–5am window is the weakest at 78.2%, 4 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 August delays on SEA to BWI?
August is the weakest month at 66.7% on time, compared with 94.7% in April. Across the year that is 28 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
- BWI to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- Baltimore/Washington International Thurgood Marshall (BWI) delay statistics
- Alaska Airlines on SEA to BWI82.8%
- Southwest Airlines on SEA to BWI68.3%
- SEA to LAX, a related route83.4%
- ATL to BWI, a related route75.6%
- SEA to PHX, a related route79.2%
- Alaska Airlines on-time record82.8%
- Southwest Airlines on-time record68.3%
- Why the first flight of the morning is statistically safest
- Worst months to fly in the US, ranked by the data
Direction matters. SEA to BWI and BWI 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.