Carrier performance at one airport
WN→BOS
Southwest Airlines at Boston Logan International
- Departures
- 7,197
- Period
- July 2025 to June 2026
- Routes
- 7
- Rank here
- #8 of 11
Southwest Airlines at Boston 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 77.6%. The late ones land about an hour behind schedule. That rests on 7,197 flights, of which Allegiant Air flew 633 at 84.9% on time.
Measured against the airport rather than the country, Southwest Airlines runs 4 points behind the 75.7% weighted average across all carriers at BOS. That is the comparison worth making: every operator here works the same runways, the same airspace and the same weather.
Key figures
On time
71.3%
7,070 completed departures
Avg delay
63 min
Across delayed flights only
Cancelled
1.53%
At BOS, this carrier only
Rank here
#8
Of 11 carriers clearing the floor at BOS
These figures cover 7,197 flights between July 2025 and June 2026. Beyond the headline rate, 9.6% 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.
Against the competition
Every carrier at BOS, ranked
The choice of carrier is not cosmetic here. Allegiant Air arrives on time 84.9% of the time; Spirit Airlines manages 65.3%. Sample sizes sit next to every figure, because a two-point gap across 2,325 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Allegiant Air | 633 | 84.9% | 86 min | 0.47% | B+ |
| Envoy Air | 2,013 | 79.9% | 74 min | 2.24% | B |
| United Airlines | 12,917 | 78.6% | 76 min | 1.90% | B |
| American Airlines | 16,933 | 78.3% | 91 min | 2.56% | B |
| Republic Airways | 33,650 | 78.1% | 67 min | 3.88% | B− |
| Delta Air Lines | 26,419 | 76.8% | 73 min | 2.03% | B |
| JetBlue Airways | 37,487 | 72.0% | 70 min | 2.51% | C |
| Southwest Airlines (this page) | 7,197 | 71.3% | 63 min | 1.53% | C |
| Alaska Airlines | 2,486 | 71.2% | 53 min | 1.17% | C |
| Frontier Airlines | 931 | 70.3% | 60 min | 1.83% | C |
| Spirit Airlines | 2,325 | 65.3% | 79 min | 4.82% | C− |
Spirit Airlines cancels 4.8% of what it schedules here, the highest in the table. A cancelled flight never appears in an on-time rate, so read that column alongside the punctuality one rather than after it.
Route by route
Where Southwest Airlines flies from BOS
Southwest Airlines operates 7 routes out of BOS with enough volume to report. Route records inside one carrier at one airport still spread widely, because a short shuttle and a transcontinental have very different exposure to a late inbound.
| Route | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| BOS to BWI · Baltimore | 2,370 | 77.8% | 72 min | 2.28% | B |
| BOS to MDW · Chicago | 1,382 | 73.1% | 62 min | 1.81% | C |
| BOS to BNA · Nashville | 996 | 67.0% | 61 min | 1.20% | C |
| BOS to STL · St. Louis | 935 | 72.4% | 62 min | 0.96% | C+ |
| BOS to DEN · Denver | 910 | 64.8% | 54 min | 0.88% | D+ |
| BOS to AUS · Austinthin sample | 282 | 62.5% | 54 min | 0.71% | D+ |
| BOS to DAL · Dallasthin sample | 260 | 53.1% | 64 min | 0.00% | F+ |
Departure window
Best time of day for this operation
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 52 points, against 20 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,869 flights92.7%
- 8am–11am954 flights89.2%
- 11am–2pm1,103 flights76.4%
- 2pm–5pm1,312 flights60.9%
- 5pm–8pm1,567 flights46.8%
- 8pm–5am392 flights41.0%
Scale runs 35% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 41.0% on time, against 92.7% 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 1,869 flights scheduled in it.
Across the year
Seasonal pattern
Delays peak in September, when the on-time rate falls to 61.7%. February is the strongest month at 85.1%. Moving a flexible trip across that boundary buys 23 points. June was the busiest month here, with 722 flights.
Delay causes
What holds this operation up
- 58%Late-arriving aircraft
- 22%Carrier
- 16%National Airspace System
- 3%Extreme weather
- 0%Security
58% 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 127,000 reported delay minutes here, that single category outweighs weather by 17 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 127,020 reported delay minutes.
Cancellations sit at 1.53% against a national 1.81%, which is ordinary. Diversions add another 0.24%.
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.6% 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.
The sample behind these figures is 7,197 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.
Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 85.1% on time and September 61.7%, a swing of 23 points. If the dates move at all, move them out of September before you think about anything else. 7,070 completed flights over 12 months sit behind that.
Common questions
Southwest Airlines at BOS
How often is Southwest Airlines at BOS delayed?
Roughly one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 28.7% of the 7,197 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on Southwest Airlines at BOS?
Allegiant Air leads at 84.9% on time across 633 flights. Spirit Airlines is at the other end on 65.3%, a gap of 20 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on Southwest Airlines at BOS?
The 5am–8am departure window is the strongest at 92.7% on time. The 8pm–5am window is the weakest at 41.0%, 52 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are September delays on Southwest Airlines at BOS?
September is the weakest month at 61.7% on time, compared with 85.1% in February. Across the year that is 23 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.