Route reliability record

SEA→LAS

Seattle to Las Vegas

Flights: 5,650
Period: July 2025 to June 2026
Distance: 867 mi
Carriers: 6

This route lands a B+, level with the national rate of 77.6%. Roughly one flight in four arrive 15 minutes late or worse, and those flights are late by about 55 minutes on average. That is a workable record, not a spotless one. That rests on 5,650 flights, of which Delta Air Lines flew 1,738 at 83.6% on time.

Delta Air Lines is the most reliable of the three carriers covered here at 83.6% on time across 1,738 flights.

On time

77.7%

Arrivals under 15 minutes late, of 5,597 completed flights

Avg delay

54 min

Across delayed arrivals only, not all flights

Cancelled

0.83%

National rate is 1.81%

Best carrier

Delta

83.6% on time across 1,738 flights

These figures cover 5,650 flights between July 2025 and June 2026. The median arrival is 4 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.

Carrier by carrier

Which airline is most reliable on SEA to LAS

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 83.6% of the time; Southwest Airlines manages 69.2%. Sample sizes sit next to every figure, because a two-point gap across 976 flights means less than a ten-point one.

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	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+

The spread between Delta and Southwest is 14 points, wide enough that it should decide the booking. On a hundred trips that is 14 more arrivals inside the on-time window.

Departure window

The best time of day to leave

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 25 points, against 14 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am796 flights92.0%
8am–11am1,003 flights85.2%
11am–2pm1,075 flights77.0%
2pm–5pm1,068 flights72.5%
5pm–8pm1,017 flights67.3%
8pm–5am691 flights74.5%

Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 92.0% of the time, against 67.3% for the evening window. That is 25 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 1,075 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 15 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.

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

July is the worst month at 69.1% on time, 15 points below April, the best at 84.4%. 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. July was the busiest month here, with 521 flights.

Across the week, Saturday is the strongest day at 82.8% on time and Friday the weakest at 73.9%. 9 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 68,000 reported delay minutes.

Carrier
40%
Late-arriving aircraft
32%
National Airspace System
26%
Extreme weather
2%
Security
1%

The largest share of delay minutes, 40%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 27,000 of the 68,000 delay minutes reported here. The split is drawn from 67,936 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 92.0% on time here.

Cancellations are rare at 0.83%, 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 actually costs

5.8% 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 are the about 55 minutes kind, 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 is a different operation and performs like one: it runs 82.3% on time across 5,649 flights, 5 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 5 points of difference.

The sample behind these figures is 5,650 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.

What to do with this

Booking this route

Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 84.4% on time and July 69.1%, a swing of 15 points. If the dates move at all, move them out of July before you think about anything else. 5,597 completed flights over 12 months sit behind that.

Common questions

SEA to LAS questions

How often is SEA to LAS delayed?

Roughly one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.3% of the 5,650 flights in this analysis, against 22.4% nationally. Delayed flights are late by about 55 minutes on average.

Which airline is most reliable on SEA to LAS?

Delta Air Lines leads at 83.6% on time across 1,738 flights. Southwest Airlines is at the other end on 69.2%, a gap of 14 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 SEA to LAS?

The 5am–8am departure window is the strongest at 92.0% on time. The 5pm–8pm window is the weakest at 67.3%, 25 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 July delays on SEA to LAS?

July is the weakest month at 69.1% on time, compared with 84.4% in April. Across the year that is 15 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. SEA to LAS and LAS to SEA are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures