Carrier route record
WNBOS→BWI
Southwest Airlines · Boston to Baltimore
- Flights
- 2,370
- 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 BOS to BWI lands a B, level with the national rate of 77.6%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 2,370 flights, with a median arrival 7 minutes early.
The US average over the same twelve months is 77.6%, 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
77.8%
Arrivals under 15 minutes late, of 2,316 completed flights
Avg delay
72 min
Across delayed arrivals only, not all flights
Cancelled
2.28%
National rate is 1.81%
Whole route
78.9%
Every carrier on BOS to BWI, 3,551 flights
These figures cover 2,370 flights between July 2025 and June 2026. Beyond the headline rate, 8.2% 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 BOS to BWI
Southwest flew 2,370 of the 3,551 flights on BOS to BWI, most of the route. Its 77.8% on time is about level with the route as a whole at 78.9%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from Republic at 81.9% to Spirit at 73.0%. 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 | 1,086 | 81.9% | 76 min | 3.31% | B− |
| Southwest Airlines (this page) | 2,370 | 77.8% | 72 min | 2.28% | B |
| Spirit Airlinesthin sample | 95 | 73.0% | 67 min | 6.32% | 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 51 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–8am566 flights94.6%
- 8am–11am400 flights90.8%
- 11am–2pm367 flights84.2%
- 2pm–5pm399 flights74.8%
- 5pm–8pm383 flights57.8%
- 8pm–5am255 flights44.0%
Scale runs 35% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 44.0% on time, against 94.6% 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 566 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. October was the busiest month here, with 230 flights.
Across the week, Wednesday is the strongest day at 84.6% on time and Sunday the weakest at 67.6%. 17 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 60% of the 37,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 60%Late-arriving aircraft
- 21%Carrier
- 14%National Airspace System
- 5%Extreme weather
- 0%Security
60% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 37,000 reported delay minutes here, that single category outweighs weather by 11 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 36,896 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 94.6% on time here.
Cancellations sit at 2.28% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
8.2% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last a little over 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 72.4% on time across 2,372 flights, 5 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 5 points of difference.
The sample behind these figures is 2,370 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. 2,316 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 BWI81.9%
- 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 7.04 million flight records
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.