Carrier route record
WNBWI→BOS
Southwest Airlines · Baltimore to Boston
- Flights
- 2,372
- Period
- July 2025 to June 2026
- Share of route
- 67%
- Carriers
- 3
Historical statistics for July 2025 to June 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, 5 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 2,372 flights, with a median arrival 3 minutes early.
The national on-time rate over the same period is 77.6%, so Southwest on BWI to BOS runs 5 points behind the country as a whole. Across a thousand flights that is about 52 extra late arrivals.
Key figures
On time
72.4%
Arrivals under 15 minutes late, of 2,315 completed flights
Avg delay
63 min
Across delayed arrivals only, not all flights
Cancelled
2.36%
National rate is 1.81%
Whole route
74.8%
Every carrier on BWI to BOS, 3,556 flights
These figures cover 2,372 flights between July 2025 and June 2026. Beyond the headline rate, 9.5% 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 BOS
Southwest flew 2,372 of the 3,556 flights on BWI to BOS, most of the route. Its 72.4% on time is 2 points worse than the route as a whole, which runs 74.8%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from Republic at 80.8% to Spirit at 68.5%. 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 |
|---|---|---|---|---|---|
| Republic Airways | 1,086 | 80.8% | 84 min | 3.13% | B− |
| Southwest Airlines (this page) | 2,372 | 72.4% | 63 min | 2.36% | C |
| Spirit Airlinesthin sample | 98 | 68.5% | 64 min | 6.12% | 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 42 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–8am353 flights93.3%
- 8am–11am529 flights90.6%
- 11am–2pm282 flights72.7%
- 2pm–5pm481 flights58.6%
- 5pm–8pm296 flights51.1%
- 8pm–5am431 flights62.0%
Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 51.1% on time, against 93.3% 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 529 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. October was the busiest month here, with 229 flights.
Across the week, Saturday is the strongest day at 79.7% on time and Sunday the weakest at 66.3%. 13 points is a smaller lever than departure hour, but it is free.
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 40,000 reported delay minutes.
- 39%National Airspace System
- 31%Late-arriving aircraft
- 27%Carrier
- 3%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 40,000, against a national NAS share of 21%. The split is drawn from 40,133 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 93.3% on time here.
Cancellations sit at 2.36% against a national 1.81%, which is ordinary. Diversions add another 0.04%.
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. 9.5% 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 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 77.8% on time across 2,370 flights, 5 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 5 points of difference.
The sample behind these figures is 2,372 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. 2,315 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 BOS80.8%
- Southwest Airlines network-wide record
- Baltimore/Washington International Thurgood Marshall (BWI) delay statistics
- Boston Logan International (BOS) delay statistics
- The best time of day to fly, according to 7.04 million flight records
- How often a connection fails at the major US hubs
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.