Carrier route record
WNBOS→BWI
Southwest Airlines · Boston to Baltimore
- Flights
- 2,413
- 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 BOS to BWI lands a B, level with the national rate of 77.3%. About one flight in four arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 2,413 flights, with a median arrival 7 minutes early.
The US average over the same twelve months is 77.3%, so there is little to separate Southwest on BOS to BWI from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
76.8%
Arrivals under 15 minutes late, of 2,348 completed flights
Avg delay
67 min
Across delayed arrivals only, not all flights
Cancelled
2.32%
National rate is 1.89%
Whole route
78.3%
Every carrier on BOS to BWI, 3,536 flights
These figures cover 2,413 flights between September 2025 and August 2026. Beyond the headline rate, 8.2% 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 BOS to BWI
Southwest flew 2,413 of the 3,536 flights on BOS to BWI, most of the route. Its 76.8% on time is 2 points worse than the route as a whole, which runs 78.3%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from Republic at 81.8% to Spirit at 75.0%. 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 | 1,099 | 81.8% | 68 min | 4.28% | B− |
| Southwest Airlines (this page) | 2,413 | 76.8% | 67 min | 2.32% | B |
| Spirit Airlinesthin sample | 24 | 75.0% | 78 min | 0.00% | B+ |
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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 48 points, against half a point between the best and worst carrier.
- 5am–8am548 flights94.5%
- 8am–11am395 flights92.0%
- 11am–2pm355 flights84.9%
- 2pm–5pm430 flights70.8%
- 5pm–8pm406 flights57.1%
- 8pm–5am279 flights46.3%
Scale runs 40% to 100%.
The 8pm–5am window is where this operation falls apart: 46.3% on time, against 94.5% 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 5am–8am window is the busiest, with 548 flights scheduled in it.
Across the year
Southwest on BOS to BWI through the year
Delays peak in October, when the on-time rate falls to 66.7%. February is the strongest month at 92.2%. Moving a flexible trip across that boundary buys 26 points. August was the busiest month here, with 233 flights.
Across the week, Tuesday is the strongest day at 83.3% on time and Sunday the weakest at 68.2%, a spread of 15 points.
Arrival by arrival
How late Southwest on BOS to BWI runs when it is late
Southwest on BOS to BWI often beats the schedule: 716 of 2,348 completed flights, 30%, arrived 15 minutes or more early. The 545 late arrivals split 171 under half an hour, 182 between 30 and 60 minutes, and 192 an hour or more.
- 15+ min early716 flights30.5%
- Within 15 min1,087 flights46.3%
- 15–29 min late171 flights7.3%
- 30–59 min late182 flights7.8%
- 1–2 hours late116 flights4.9%
- 2+ hours late76 flights3.2%
Scale runs 0% to 100%.
Share of 2,348 completed flights by arrival against schedule.
220 of 735 late departures made up the time and arrived on time, 30% of them. Only 30 left on time and still arrived late.
The worst days
Worst days for Southwest on BOS to BWI
The latest arrival of the period was on 4 January 2026, 7 hours 18 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). Three of the five worst days fell in September 2025.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 4 January 2026 | 7 hours 18 minutes | Carrier |
| 6 September 2025 | 5 hours 47 minutes | Extreme weather |
| 18 July 2026 | 5 hours 47 minutes | National Airspace System |
| 24 September 2025 | 5 hours 32 minutes | Late-arriving aircraft |
| 25 September 2025 | 5 hours 30 minutes | Late-arriving aircraft |
Delay causes
Why Southwest runs late on this route
Late-arriving aircraft accounts for 64% of the 37,000 delay minutes carriers reported here, and the remaining four split what is left.
- 64%Late-arriving aircraft
- 23%Carrier
- 10%National Airspace System
- 3%Extreme weather
- 0%Security
64% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 37,000 reported delay minutes here, that single category outweighs weather by 25 to one. The split is drawn from 36,518 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 94.5% on time here.
Cancellations sit at 2.32% against a national 1.89%, which is ordinary. Diversions add another 0.37%.
Connections and stage length
What a delay here costs
8.2% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.
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 71.1% on time across 2,415 flights, 6 points below 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 2,413 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 BOS to BWI
Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 92.2% on time and October 66.7%, a swing of 26 points. If the dates move at all, move them out of October before you think about anything else. 2,348 completed flights over 12 months sit behind that.
Related
Where to go next
- BOS to BWI, every carrier
- Southwest on BWI to BOS, the return leg
- Republic Airways on BOS to BWI81.8%
- Southwest Airlines network-wide record
- Boston Logan International (BOS) delay statistics
- Baltimore/Washington International Thurgood Marshall (BWI) delay statistics
- Why the first flight of the morning is statistically safest
- 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.