Carrier route record

WNSEA→BWI

Southwest Airlines · Seattle to Baltimore

Flights: 120
Period: July 2025 to June 2026
Share of route: 17%
Carriers: 2

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.

Southwest on SEA to BWI sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 9 points worse than the national rate of 77.6%. The late ones land roughly 40 minutes behind schedule. That rests on 120 flights, with a median arrival 3 minutes late.

The national on-time rate over the same period is 77.6%, so Southwest on SEA to BWI runs 9 points behind the country as a whole. Across a thousand flights that is about 93 extra late arrivals.

On time

68.3%

Arrivals under 15 minutes late, of 120 completed flights

Avg delay

41 min

Across delayed arrivals only, not all flights

Cancelled

0.00%

National rate is 1.81%

Whole route

80.4%

Every carrier on SEA to BWI, 719 flights

These figures cover 120 flights between July 2025 and June 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.

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 68.3% on time is 12 points worse than the route as a whole, which runs 80.4%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from Alaska at 82.8% to Southwest at 68.3%.

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.

On-time performance by carrier on SEA to BWI
Airline	Flights	On time	Avg delay	Cancelled	Grade
Alaska Airlines	599	82.8%	43 min	0.50%	B+
Southwest Airlines (this page)thin sample	120	68.3%	41 min	0.00%	C+

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 68.3% is the reliable figure here.

Across the year

Southwest on SEA to BWI through the year

Jul–Sep 202592 flights70.7%
Oct–Dec 20251 flights—
Apr–Jun 202627 flights—

Scale runs 60% to 75%. 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 68.3% on time across 120 flights.

Split by quarter, Southwest on SEA to BWI logged 92 flights in Jul–Sep 2025, 1 flights in Oct–Dec 2025 and 27 flights in Apr–Jun 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 68.3% annual figure is the one to use.

Delay causes

Why Southwest runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 69% of the 1,567 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.

Late-arriving aircraft
69%
National Airspace System
18%
Carrier
13%
Security
1%

69% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 1,567 reported delay minutes here, that single category outweighs weather by 69 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 1,567 reported delay minutes.

Cancellations are rare at 0.00%, below the national 1.81% and low enough to earn the plus on the grade. Almost no flights are called off; the risk here is arriving late, not not arriving.

Connections and stage length

What a delay here costs

6.7% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last roughly 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 66.7% on time across 120 flights, within 2 points 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 68.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 120 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures