Carrier route record
WNBWI→BOS
Southwest Airlines · Baltimore to Boston
- Flights
- 2,415
- Period
- September 2025 to August 2026
- Share of route
- 68%
- Carriers
- 3
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on BWI to BOS sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 6 points worse than the national rate of 77.3%. The late ones land about an hour behind schedule. That rests on 2,415 flights, with a median arrival 2 minutes early.
The national on-time rate over the same period is 77.3%, so Southwest on BWI to BOS runs 6 points behind the country as a whole. Across a thousand flights that is about 62 extra late arrivals.
Key figures
On time
71.1%
Arrivals under 15 minutes late, of 2,343 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
2.77%
National rate is 1.89%
Whole route
74.1%
Every carrier on BWI to BOS, 3,540 flights
These figures cover 2,415 flights between September 2025 and August 2026. Beyond the headline rate, 9.9% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Southwest against every carrier on BWI to BOS
Southwest flew 2,415 of the 3,540 flights on BWI to BOS, most of the route. Its 71.1% on time is 3 points worse than the route as a whole, which runs 74.1%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from Spirit at 80.8% to Southwest at 71.1%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
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 |
|---|---|---|---|---|---|
| Spirit Airlinesthin sample | 26 | 80.8% | 35 min | 0.00% | B+ |
| Republic Airways | 1,099 | 80.5% | 85 min | 4.09% | B− |
| Southwest Airlines (this page) | 2,415 | 71.1% | 61 min | 2.77% | C |
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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 41 points, against half a point between the best and worst carrier.
- 5am–8am348 flights94.1%
- 8am–11am522 flights89.9%
- 11am–2pm345 flights68.8%
- 2pm–5pm488 flights55.5%
- 5pm–8pm284 flights53.0%
- 8pm–5am428 flights60.4%
Scale runs 45% to 100%.
The 5pm–8pm window is where this operation falls apart: 53.0% on time, against 94.1% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 8am–11am window is the busiest, with 522 flights scheduled in it.
Across the year
Southwest on BWI to BOS through the year
November is the best month on the calendar at 84.8% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. August was the busiest month here, with 233 flights.
Across the week, Saturday is the strongest day at 77.4% on time and Sunday the weakest at 64.0%, a spread of 13 points.
Arrival by arrival
How late Southwest on BWI to BOS runs when it is late
The 676 late arrivals split 221 under half an hour, 223 between 30 and 60 minutes, and 232 an hour or more.
- 15+ min early493 flights21.0%
- Within 15 min1,174 flights50.1%
- 15–29 min late221 flights9.4%
- 30–59 min late223 flights9.5%
- 1–2 hours late160 flights6.8%
- 2+ hours late72 flights3.1%
Scale runs 0% to 100%.
Share of 2,343 completed flights by arrival against schedule.
187 of 810 late departures made up the time and arrived on time, 23% of them. 53 flights left on time and still arrived late.
The worst days
Worst days for Southwest on BWI to BOS
The latest arrival of the period was on 6 September 2025, 6 hours 51 minutes behind schedule; most of its delay minutes were filed as national airspace system delay. Five of the five worst days fell in September 2025.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 6 September 2025 | 6 hours 51 minutes | National Airspace System |
| 25 September 2025 | 6 hours 50 minutes | National Airspace System |
| 24 September 2025 | 5 hours 42 minutes | National Airspace System |
| 25 September 2025 | 5 hours 38 minutes | Carrier |
| 24 September 2025 | 5 hours 20 minutes | Carrier |
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 41,000 reported delay minutes.
- 39%National Airspace System
- 28%Carrier
- 28%Late-arriving aircraft
- 5%Extreme weather
- 0%Security
39% 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 16,000 minutes out of 41,000, against a national NAS share of 21%. The split is drawn from 41,359 reported delay minutes.
Cancellations run at 2.77%, against 1.89% nationally. That is roughly one flight in 40 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.
Connections and stage length
What a delay here costs
9.9% 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 369 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 5am–8am window matters as much as it does.
The return leg is a different operation and performs like one: it runs 76.8% on time across 2,413 flights, 6 points above 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 6 points of difference.
The sample behind these figures is 2,415 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
What to do with this
Booking Southwest on BWI to BOS
Put together: the calendar is the biggest lever here, not the carrier or the hour. November runs 84.8% on time and September 57.8%, a swing of 27 points. If the dates move at all, move them out of September before you think about anything else. 2,343 completed flights over 12 months sit behind that.
Related
Where to go next
- BWI to BOS, every carrier
- Southwest on BOS to BWI, the return leg
- Republic Airways on BWI to BOS80.5%
- Southwest Airlines network-wide record
- Baltimore/Washington International Thurgood Marshall (BWI) delay statistics
- Boston Logan International (BOS) delay statistics
- The US routes with the most cancellations
- The best time of day to fly, according to 7.05 million flight records
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.