Carrier route record

WNBNA→SEA

Southwest Airlines · Nashville to Seattle

Flights: 125
Period: July 2025 to June 2026
Share of route: 8%
Carriers: 3

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.

Southwest on BNA to SEA earns an F+, which is as low as this site's scale goes for a reason. Only 44.7% of flights arrive inside the 15-minute window, 33 points worse than the national rate of 77.6%. Late arrivals average roughly 50 minutes. Treat any tight connection here as a coin flip. That rests on 125 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 511 at 83.4% on time.

The national on-time rate over the same period is 77.6%, so Southwest on BNA to SEA runs 33 points behind the country as a whole. Across a thousand flights that is about 329 extra late arrivals.

On time

44.7%

Arrivals under 15 minutes late, of 123 completed flights

Avg delay

52 min

Across delayed arrivals only, not all flights

Cancelled

0.80%

National rate is 1.81%

Whole route

72.7%

Every carrier on BNA to SEA, 1,479 flights

These figures cover 125 flights between July 2025 and June 2026. Beyond the headline rate, 15.4% 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 SEA

Southwest flew 125 of the 1,479 flights on BNA to SEA, about 8% of it. Its 44.7% on time is 28 points worse than the route as a whole, which runs 72.7%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from Delta at 83.4% to Southwest at 44.7%.

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 83.4% of the time; Alaska Airlines manages 70.3%. Sample sizes sit next to every figure, because a two-point gap across 843 flights means less than a ten-point one.

On-time performance by carrier on BNA to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	511	83.4%	66 min	0.78%	B+
Alaska Airlines	843	70.3%	49 min	1.42%	C
Southwest Airlines (this page)thin sample	125	44.7%	52 min	0.80%	F+

The spread between Delta and Alaska is 13 points, wide enough that it should decide the booking. On a hundred trips that is 13 more arrivals inside the on-time window.

Departure window

When Southwest runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 125 flights.

5am–8am—
8am–11am6 flights—
11am–2pm8 flights—
2pm–5pm39 flights35.9%
5pm–8pm62 flights45.0%
8pm–5am10 flights—

Scale runs 25% to 50%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is the strongest at 45.0% on time. The full set of windows spans 9 points.

Across the year

Southwest on BNA to SEA through the year

Jul–Sep 202597 flights50.0%
Oct–Dec 20251 flights—
Apr–Jun 202627 flights—

Scale runs 40% to 55%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 44.7% on time across 125 flights.

Split by quarter, Southwest on BNA to SEA logged 97 flights in Jul–Sep 2025, 1 flights in Oct–Dec 2025 and 27 flights in Apr–Jun 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 44.7% annual figure is the one to use.

Delay causes

Why Southwest runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 56% of the 3,560 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.

Late-arriving aircraft
56%
Carrier
27%
National Airspace System
12%
Extreme weather
4%

56% 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 3,560 reported delay minutes here, that single category outweighs weather by 13 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 3,560 reported delay minutes.

Cancellations are rare at 0.80%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.

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. 15.4% 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 1,978 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 64.8% on time across 125 flights, 20 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 20 points of difference.

One caution: this is a thin sample. 125 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 SEA

Put together: treat all of this as provisional. 125 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 44.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 123 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures