Carrier route record
WNSEA→BWI
Southwest Airlines · Seattle to Baltimore
- Flights
- 120
- Period
- September 2025 to August 2026
- Share of route
- 17%
- Carriers
- 2
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on SEA to BWI draws a D+. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is about 40 minutes behind schedule. Build slack into anything you connect to. That rests on 120 flights, with a median arrival 6 minutes late.
The national on-time rate over the same period is 77.3%, so Southwest on SEA to BWI runs 17 points behind the country as a whole. Across a thousand flights that is about 168 extra late arrivals.
Key figures
On time
60.5%
Arrivals under 15 minutes late, of 119 completed flights
Avg delay
40 min
Across delayed arrivals only, not all flights
Cancelled
0.83%
National rate is 1.89%
Whole route
80.7%
Every carrier on SEA to BWI, 719 flights
These figures cover 120 flights between September 2025 and August 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.
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Carrier by carrier
Southwest against every carrier on SEA to BWI
Southwest flew 120 of the 719 flights on SEA to BWI, about 17% of it. Its 60.5% on time is 20 points worse than the route as a whole, which runs 80.7%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from Alaska at 84.8% to Southwest at 60.5%.
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 | 84.8% | 39 min | 0.67% | B+ |
| Southwest Airlines (this page)thin sample | 120 | 60.5% | 40 min | 0.83% | D+ |
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Departure window
When Southwest 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 120 flights.
There are not enough flights in each departure window to split Southwest's SEA to BWI record by time of day without the percentages moving on noise. The headline rate of 60.5% is the reliable figure here.
Across the year
Southwest on SEA to BWI through the year
- Jul–Sep 202530 flights83.3%
- Oct–Dec 20251 flights—
- Apr–Jun 202627 flights—
- Jul–Sep 202662 flights49.2%
Scale runs 40% to 90%. Rows with fewer than 30 flights show a dash.
Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 60.5% on time across 120 flights.
Split by quarter, Southwest on SEA to BWI logged 30 flights in Jul–Sep 2025, 1 flights in Oct–Dec 2025, 27 flights in Apr–Jun 2026 and 62 flights in Jul–Sep 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 60.5% annual figure is the one to use.
Arrival by arrival
How late Southwest on SEA to BWI runs when it is late
The 47 late arrivals split 19 under half an hour, 19 between 30 and 60 minutes, and 9 an hour or more. Not one arrived two hours late.
- 15+ min early20 flights16.8%
- Within 15 min52 flights43.7%
- 15–29 min late19 flights16.0%
- 30–59 min late19 flights16.0%
- 1–2 hours late9 flights7.6%
- 2+ hours late0 flights0.0%
Scale runs 0% to 100%.
Share of 119 completed flights by arrival against schedule.
7 of 48 late departures made up the time and arrived on time, 15% of them. In the other direction, 6 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at BWI.
The worst days
Worst days for Southwest on SEA to BWI
The latest arrival of the period was on 14 August 2026, 1 hour 34 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. Three of the five worst days fell in June 2026.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 14 August 2026 | 1 hour 34 minutes | Late-arriving aircraft |
| 9 June 2026 | 1 hour 32 minutes | Late-arriving aircraft |
| 9 August 2026 | 1 hour 28 minutes | Late-arriving aircraft |
| 14 June 2026 | 1 hour 25 minutes | Late-arriving aircraft |
| 10 June 2026 | 1 hour 20 minutes | Late-arriving aircraft |
Delay causes
Why Southwest runs late on this route
Late-arriving aircraft accounts for 74% of the 1,900 delay minutes carriers reported here, and the remaining four split what is left.
- 74%Late-arriving aircraft
- 13%National Airspace System
- 12%Carrier
74% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 1,900 reported delay minutes here, that single category outweighs weather by 74 to one. The split is drawn from 1,900 reported delay minutes.
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 costs
7.6% 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 about 40 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 runs 59.7% on time across 120 flights, within about 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. 120 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 Southwest on SEA to BWI
Put together: treat all of this as provisional. 120 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 60.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 119 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to BWI, every carrier
- Southwest on BWI to SEA, the return leg
- Alaska Airlines on SEA to BWI84.8%
- Southwest Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Baltimore/Washington International Thurgood Marshall (BWI) delay statistics
- Why the first flight of the morning is statistically safest
- How to read this site: grades, sample sizes, and honest caveats
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.