Carrier route record

WNSEA→LAS

Southwest Airlines · Seattle to Las Vegas

Flights: 976
Period: July 2025 to June 2026
Share of route: 17%
Carriers: 6

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

Southwest on SEA to LAS sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 8 points worse than the national rate of 77.6%. The late ones land roughly 50 minutes behind schedule. That rests on 976 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 1,738 at 83.6% on time.

The national on-time rate over the same period is 77.6%, so Southwest on SEA to LAS runs 8 points behind the country as a whole. Across a thousand flights that is about 84 extra late arrivals.

On time

69.2%

Arrivals under 15 minutes late, of 971 completed flights

Avg delay

48 min

Across delayed arrivals only, not all flights

Cancelled

0.51%

National rate is 1.81%

Whole route

77.7%

Every carrier on SEA to LAS, 5,650 flights

These figures cover 976 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 LAS

Southwest flew 976 of the 5,650 flights on SEA to LAS, about 17% of it. Its 69.2% on time is 9 points worse than the route as a whole, which runs 77.7%. Ranked by on-time rate it is number four of six carriers on the route, where the range runs from SkyWest at 100.0% to Spirit at 67.4%. Three of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The two carriers here are closely matched: 6 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

On-time performance by carrier on SEA to LAS
Airline	Flights	On time	Avg delay	Cancelled	Grade
SkyWest Airlinesthin sample	9	100.0%	—	0.00%	A+
Delta Air Lines	1,738	83.6%	56 min	0.86%	B+
Alaska Airlines	2,638	78.0%	47 min	0.91%	B+
Southwest Airlines (this page)	976	69.2%	48 min	0.51%	C+
Frontier Airlinesthin sample	246	67.9%	128 min	1.22%	C
Spirit Airlinesthin sample	43	67.4%	39 min	0.00%	C+

No carrier stands out. Delta tops the table at 83.6%, 6 points clear of the bottom, which is inside the range this kind of sample moves year to year.

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 48 points, against 6 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am286 flights92.2%
8am–11am114 flights86.8%
11am–2pm211 flights60.2%
2pm–5pm194 flights57.5%
5pm–8pm171 flights43.9%
8pm–5am—

Scale runs 35% to 100%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 43.9% on time, against 92.2% 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 286 flights scheduled in it.

Across the year

Southwest on SEA to LAS through the year

Darker means more delays. Figures are on-time percentages.January best, July worst

July is the worst month at 55.4% on time, 32 points below January, the best at 87.7%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. May was the busiest month here, with 93 flights.

Across the week, Saturday is the strongest day at 76.0% on time and Friday the weakest at 62.5%. 14 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 45% of the 14,000 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.

Late-arriving aircraft
45%
Carrier
33%
National Airspace System
18%
Security
3%
Extreme weather
1%

45% 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 14,000 reported delay minutes here, that single category outweighs weather by 45 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 14,407 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 92.2% on time here.

Cancellations are rare at 0.51%, 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

6.7% 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 roughly 50 minutes, which a normal layover absorbs.

The 867 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 runs 71.0% on time across 977 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

One caution: this is a thin sample. 976 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 LAS

Put together: treat all of this as provisional. 976 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 69.2% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 971 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