Carrier route record

WNSEA→BNA

Southwest Airlines · Seattle to Nashville

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 SEA to BNA draws a D+. About one flight in three arrives at least 15 minutes late, and the typical late arrival is about 40 minutes behind schedule. Build slack into anything you connect to. That rests on 125 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 511 at 84.6% on time.

The national on-time rate over the same period is 77.6%, so Southwest on SEA to BNA runs 13 points behind the country as a whole. Across a thousand flights that is about 128 extra late arrivals.

On time

64.8%

Arrivals under 15 minutes late, of 125 completed flights

Avg delay

39 min

Across delayed arrivals only, not all flights

Cancelled

0.00%

National rate is 1.81%

Whole route

78.6%

Every carrier on SEA to BNA, 1,479 flights

These figures cover 125 flights between July 2025 and June 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.

Carrier by carrier

Southwest against every carrier on SEA to BNA

Southwest flew 125 of the 1,479 flights on SEA to BNA, about 8% of it. Its 64.8% on time is 14 points worse than the route as a whole, which runs 78.6%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from Delta at 84.6% to Southwest at 64.8%.

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 84.6% of the time; Alaska Airlines manages 77.0%. 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 SEA to BNA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	511	84.6%	61 min	0.59%	B+
Alaska Airlines	843	77.0%	43 min	1.07%	B
Southwest Airlines (this page)thin sample	125	64.8%	39 min	0.00%	D+

Delta leads Alaska by 8 points. Real, but small enough that a better departure time on the weaker carrier can outweigh 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 23 points, against 8 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am5 flights—
8am–11am58 flights75.9%
11am–2pm—
2pm–5pm—
5pm–8pm—
8pm–5am62 flights53.2%

Scale runs 45% to 80%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 53.2% on time, against 75.9% 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 8pm–5am window is the busiest, with 62 flights scheduled in it.

Across the year

Southwest on SEA to BNA through the year

Jul–Sep 202597 flights70.1%
Oct–Dec 20251 flights—
Apr–Jun 202627 flights—

Scale runs 60% to 75%. 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 64.8% on time across 125 flights.

Split by quarter, Southwest on SEA to BNA 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 64.8% 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 67% of the 1,732 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
67%
Carrier
20%
National Airspace System
13%

67% 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 1,732 reported delay minutes here, that single category outweighs weather by 67 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 1,732 reported delay minutes.

The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 75.9% on time here.

Cancellations are rare at 0.00%, below the national 1.81% and low enough to earn the plus on the grade. Almost no flights are called off; the risk here is arriving late, not not arriving.

Connections and stage length

What a delay here costs

Badly late arrivals are rare here: only 4.0% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

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 44.7% on time across 125 flights, 20 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 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 SEA to BNA

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 64.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 125 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