Carrier route record
WNBNA→BOS
Southwest Airlines · Nashville to Boston
- Flights
- 997
- Period
- July 2025 to June 2026
- Share of route
- 34%
- Carriers
- 6
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on BNA to BOS draws a D. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is roughly 55 minutes behind schedule. Build slack into anything you connect to. That rests on 997 flights. The strongest carrier on the route with a full sample, Republic Airways, flew 500 at 80.9% on time.
Republic Airways is the most reliable of the three carriers covered here at 80.9% on time across 500 flights.
Key figures
On time
60.6%
Arrivals under 15 minutes late, of 982 completed flights
Avg delay
53 min
Across delayed arrivals only, not all flights
Cancelled
1.40%
National rate is 1.81%
Whole route
69.0%
Every carrier on BNA to BOS, 2,946 flights
These figures cover 997 flights between July 2025 and June 2026. Beyond the headline rate, 12.1% 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 BNA to BOS
Southwest flew 997 of the 2,946 flights on BNA to BOS, about 34% of it. Its 60.6% on time is 8 points worse than the route as a whole, which runs 69.0%. Ranked by on-time rate it is last of six carriers on the route, where the range runs from American at 100.0% to Southwest at 60.6%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The choice of carrier is not cosmetic here. Republic Airways arrives on time 80.9% of the time; JetBlue Airways manages 70.5%. Sample sizes sit next to every figure, because a two-point gap across 874 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlinesthin sample | 2 | 100.0% | — | 0.00% | A+ |
| Republic Airways | 500 | 80.9% | 90 min | 3.60% | B− |
| Delta Air Lines | 533 | 71.5% | 105 min | 0.75% | C+ |
| JetBlue Airways | 874 | 70.5% | 70 min | 2.29% | C |
| Spirit Airlinesthin sample | 40 | 65.8% | 125 min | 5.00% | C− |
| Southwest Airlines (this page) | 997 | 60.6% | 53 min | 1.40% | D |
Republic Airways cancels 3.6% 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.
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 37 points, against 10 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1 flights—
- 8am–11am292 flights81.8%
- 11am–2pm159 flights53.8%
- 2pm–5pm169 flights47.9%
- 5pm–8pm239 flights56.4%
- 8pm–5am137 flights45.1%
Scale runs 35% to 85%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 45.1% on time, against 81.8% for the 8am–11am 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 292 flights scheduled in it.
Across the year
Southwest on BNA to BOS through the year
Delays peak in May, when the on-time rate falls to 45.7%. January is the strongest month at 80.6%. Moving a flexible trip across that boundary buys 35 points. October was the busiest month here, with 111 flights.
Across the week, Saturday is the strongest day at 75.0% on time and Thursday the weakest at 51.7%. 23 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 42% of the 20,000 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.
- 42%Late-arriving aircraft
- 36%National Airspace System
- 19%Carrier
- 3%Extreme weather
42% 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 20,000 reported delay minutes here, that single category outweighs weather by 16 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 20,332 reported delay minutes.
36% 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 7,279 minutes out of 20,000, against a national NAS share of 21%.
Cancellations sit at 1.40% against a national 1.81%, which is ordinary. Diversions add another 0.10%.
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. 12.1% 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 942 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg is a different operation and performs like one: it runs 67.0% on time across 996 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.
One caution: this is a thin sample. 997 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Southwest on BNA to BOS
Put together: treat all of this as provisional. 997 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 60.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 982 completed flights over 12 months sit behind that.
Related
Where to go next
- BNA to BOS, every carrier
- Southwest on BOS to BNA, the return leg
- Republic Airways on BNA to BOS80.9%
- Delta Air Lines on BNA to BOS71.5%
- JetBlue Airways on BNA to BOS70.5%
- Southwest Airlines network-wide record
- Nashville International (BNA) delay statistics
- Boston Logan International (BOS) delay statistics
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
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.