Carrier route record

WNBWI→SEA

Southwest Airlines · Baltimore to Seattle

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 BWI to SEA draws a C+. About one flight in three arrives at least 15 minutes late, and the typical late arrival is a little over an hour behind schedule. Build slack into anything you connect to. That rests on 120 flights, with a median arrival 5 minutes late.

The national on-time rate over the same period is 77.6%, so Southwest on BWI to SEA runs 11 points behind the country as a whole. Across a thousand flights that is about 109 extra late arrivals.

On time

66.7%

Arrivals under 15 minutes late, of 120 completed flights

Avg delay

74 min

Across delayed arrivals only, not all flights

Cancelled

0.00%

National rate is 1.81%

Whole route

68.4%

Every carrier on BWI to SEA, 719 flights

These figures cover 120 flights between July 2025 and June 2026. Beyond the headline rate, 10.0% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

Carrier by carrier

Southwest against every carrier on BWI to SEA

Southwest flew 120 of the 719 flights on BWI to SEA, about 17% of it. Its 66.7% on time is 2 points worse than the route as a whole, which runs 68.4%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from Alaska at 68.8% to Southwest at 66.7%.

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 BWI to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Alaska Airlines	599	68.8%	48 min	0.83%	C+
Southwest Airlines (this page)thin sample	120	66.7%	74 min	0.00%	C+

Departure window

When Southwest runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 38 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am—
8am–11am36 flights80.6%
11am–2pm5 flights—
2pm–5pm42 flights42.9%
5pm–8pm37 flights81.1%
8pm–5am—

Scale runs 35% to 85%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is the strongest at 81.1% on time. The full set of windows spans 38 points.

Across the year

Southwest on BWI to SEA through the year

Jul–Sep 202592 flights71.7%
Oct–Dec 20251 flights—
Apr–Jun 202627 flights—

Scale runs 65% 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 66.7% on time across 120 flights.

Split by quarter, Southwest on BWI to SEA 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 66.7% annual figure is the one to use.

Delay causes

Why Southwest runs late on this route

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 2,963 reported delay minutes.

National Airspace System
33%
Late-arriving aircraft
31%
Extreme weather
20%
Carrier
17%

Extreme weather accounts for 20% 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 3.1 times the usual weather exposure. The split is drawn from 2,963 reported delay minutes.

33% 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 977 minutes out of 2,963, against a national NAS share of 21%.

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

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 10.0% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

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 68.3% 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 BWI to SEA

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 66.7% 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