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DelayAtlas

Carrier route record

WNBWI→SEA

Southwest Airlines · Baltimore to Seattle

Flights
120
Period
September 2025 to August 2026
Share of route
17%
Carriers
2
D+GRADE

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

Southwest on BWI to SEA draws a D+. Roughly one flight in two arrives at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 120 flights, with a median arrival 8 minutes late.

The national on-time rate over the same period is 77.3%, so Southwest on BWI to SEA runs 18 points behind the country as a whole. Across a thousand flights that is about 176 extra late arrivals.

Key figures

On time

59.7%

Arrivals under 15 minutes late, of 119 completed flights

Avg delay

64 min

Across delayed arrivals only, not all flights

Cancelled

0.83%

National rate is 1.89%

Whole route

66.8%

Every carrier on BWI to SEA, 719 flights

These figures cover 120 flights between September 2025 and August 2026. Beyond the headline rate, 14.3% of arrivals land a full hour or more behind schedule, against 8.3% nationally.

Fare search by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.

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 59.7% on time is 7 points worse than the route as a whole, which runs 66.8%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from Alaska at 68.2% to Southwest at 59.7%.

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
AirlineFlightsOn timeAvg delayCancelledGrade
Alaska Airlines59968.2%49 min0.83%C+
Southwest Airlines (this page)thin sample12059.7%64 min0.83%D+

Timetable by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.

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 27 points, against half a point between the best and worst carrier.

  • 5am–8am—
  • 8am–11am50 flights71.4%
  • 11am–2pm17 flights—
  • 2pm–5pm36 flights44.4%
  • 5pm–8pm17 flights—
  • 8pm–5am—

Scale runs 35% to 75%. Rows with fewer than 30 flights show a dash.

Book the morning departure. Flights leaving between 8am–11am arrive on time 71.4% of the time, against 44.4% for the afternoon window. That is 27 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 50 flights scheduled in it.

Across the year

Southwest on BWI to SEA through the year

  • Jul–Sep 202530 flights86.7%
  • Oct–Dec 20251 flights—
  • Apr–Jun 202627 flights—
  • Jul–Sep 202662 flights50.8%

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 59.7% on time across 120 flights.

Split by quarter, Southwest on BWI to SEA 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 59.7% annual figure is the one to use.

Arrival by arrival

How late Southwest on BWI to SEA runs when it is late

The 48 late arrivals split 15 under half an hour, 16 between 30 and 60 minutes, and 17 an hour or more.

  • 15+ min early21 flights17.6%
  • Within 15 min50 flights42.0%
  • 15–29 min late15 flights12.6%
  • 30–59 min late16 flights13.4%
  • 1–2 hours late10 flights8.4%
  • 2+ hours late7 flights5.9%

Scale runs 0% to 100%.

Share of 119 completed flights by arrival against schedule.

11 of 43 late departures made up the time and arrived on time, 26% of them. In the other direction, 16 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 SEA.

The worst days

Worst days for Southwest on BWI to SEA

The latest arrival of the period was on 9 July 2026, 6 hours 40 minutes behind schedule; most of its delay minutes were filed as extreme weather. Three of the five worst days fell in June 2026.

The latest arrivals of Southwest on BWI to SEA in the period
DateArrived late byLargest filed cause
9 July 20266 hours 40 minutesExtreme weather
6 September 20253 hours 55 minutesLate-arriving aircraft
14 June 20263 hours 9 minutesNational Airspace System
11 June 20262 hours 48 minutesCarrier
13 June 20262 hours 35 minutesLate-arriving aircraft

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 3,074 reported delay minutes.

  • National Airspace System
    37%
  • Late-arriving aircraft
    28%
  • Carrier
    23%
  • Extreme weather
    12%

Extreme weather accounts for 12% 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 2.0 times the usual weather exposure. The split is drawn from 3,074 reported delay minutes.

37% 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 1,134 minutes out of 3,074, 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 costs

14.3% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection 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 60.5% 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 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 59.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 119 completed flights over 12 months sit behind that.

Related

Where to go next

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.