Carrier performance at one airport
WN→SEA
Southwest Airlines at Seattle-Tacoma International
- Departures
- 8,194
- Period
- September 2025 to August 2026
- Routes
- 14
- Rank here
- #8 of 10
Southwest Airlines at Seattle sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 9 points worse than the national rate of 77.3%. The late ones land about 50 minutes behind schedule. That rests on 8,194 flights, of which Envoy Air flew 760 at 85.3% on time.
Measured against the airport rather than the country, Southwest Airlines runs 11 points behind the 79.6% weighted average across all carriers at SEA. That is the comparison worth making: every operator here works the same runways, the same airspace and the same weather.
Key figures
On time
68.2%
8,137 completed departures
Avg delay
50 min
Across delayed flights only
Cancelled
0.44%
At SEA, this carrier only
Rank here
#8
Of 10 carriers clearing the floor at SEA
These figures cover 8,194 flights between September 2025 and August 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.
Against the competition
Every carrier at SEA, ranked
The choice of carrier is not cosmetic here. Envoy Air arrives on time 85.3% of the time; JetBlue Airways manages 53.6%. Sample sizes sit next to every figure, because a two-point gap across 413 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Envoy Air | 760 | 85.3% | 74 min | 0.00% | A+ |
| SkyWest Airlines | 28,580 | 84.9% | 60 min | 0.75% | B+ |
| Delta Air Lines | 32,382 | 80.7% | 64 min | 1.11% | B |
| United Airlines | 8,683 | 79.9% | 74 min | 0.75% | B+ |
| American Airlines | 6,768 | 79.7% | 97 min | 1.73% | B |
| Alaska Airlines | 76,970 | 78.5% | 47 min | 0.89% | B+ |
| Frontier Airlines | 1,397 | 75.8% | 89 min | 2.22% | B |
| Southwest Airlines (this page) | 8,194 | 68.2% | 50 min | 0.44% | C+ |
| Hawaiian Airlines | 612 | 65.8% | 93 min | 1.47% | C |
| JetBlue Airways | 413 | 53.6% | 101 min | 4.60% | F− |
JetBlue Airways cancels 4.6% 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.
Route by route
Where Southwest Airlines flies from SEA
Southwest Airlines operates 14 routes out of SEA with enough volume to report. Route records inside one carrier at one airport still spread widely, because a short shuttle and a transcontinental have very different exposure to a late inbound.
| Route | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| SEA to DEN · Denver | 1,342 | 67.3% | 55 min | 0.67% | C+ |
| SEA to SMF · Sacramento | 1,139 | 73.3% | 48 min | 0.35% | C+ |
| SEA to OAK · Oakland | 1,088 | 69.8% | 52 min | 0.28% | C+ |
| SEA to PHX · Phoenix | 1,042 | 65.1% | 49 min | 0.77% | C+ |
| SEA to LAS · Las Vegas | 977 | 70.3% | 52 min | 0.51% | C+ |
| SEA to SJC · San Jose | 903 | 70.5% | 46 min | 0.22% | C+ |
| SEA to MDW · Chicago | 678 | 82.9% | 42 min | 0.44% | B+ |
| SEA to DAL · Dallasthin sample | 219 | 38.5% | 56 min | 0.00% | F+ |
| SEA to SAN · San Diegothin sample | 208 | 47.1% | 45 min | 0.00% | F+ |
| SEA to BNA · Nashvillethin sample | 120 | 60.0% | 39 min | 0.00% | D+ |
| SEA to BWI · Baltimorethin sample | 120 | 60.5% | 40 min | 0.83% | D+ |
| SEA to HOU · Houstonthin sample | 120 | 57.5% | 44 min | 0.00% | D+ |
| SEA to STL · St. Louisthin sample | 103 | 73.5% | 55 min | 0.97% | C+ |
| SEA to AUS · Austinthin sample | 89 | 42.7% | 57 min | 0.00% | F+ |
Departure window
Best time of day for this operation
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 48 points, against 32 points between the best and worst carrier.
- 5am–8am2,099 flights94.1%
- 8am–11am1,293 flights81.5%
- 11am–2pm1,540 flights56.4%
- 2pm–5pm1,247 flights45.9%
- 5pm–8pm1,081 flights53.4%
- 8pm–5am934 flights58.0%
Scale runs 35% to 100%.
Book the early departure. Flights leaving between 5am–8am arrive on time 94.1% of the time, against 45.9% for the afternoon window. That is 48 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 2,099 flights scheduled in it.
Across the year
Seasonal pattern
August is the worst month at 53.3% on time, 34 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. August was the busiest month here, with 994 flights.
Delay causes
What holds this operation up
- 52%Late-arriving aircraft
- 30%Carrier
- 15%National Airspace System
- 1%Extreme weather
- 1%Security
52% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 130,000 reported delay minutes here, that single category outweighs weather by 43 to one. The split is drawn from 129,977 reported delay minutes.
Cancellations are rare at 0.44%, below the national 1.89% 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.
7.6% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about 50 minutes, which a normal layover absorbs.
The sample behind these figures is 8,194 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.
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 87.7% on time and August 53.3%, a swing of 34 points. If the dates move at all, move them out of August before you think about anything else. 8,137 completed flights over 12 months sit behind that.
Common questions
Southwest Airlines at SEA
How often is Southwest Airlines at SEA delayed?
About one flight in three arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 31.8% of the 8,194 flights in this analysis, against 22.7% nationally. Delayed flights are late by about 50 minutes on average.
Which airline is most reliable on Southwest Airlines at SEA?
Envoy Air leads at 85.3% on time across 760 flights. JetBlue Airways is at the other end on 53.6%, a gap of 32 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 Southwest Airlines at SEA?
The 5am–8am departure window is the strongest at 94.1% on time. The 2pm–5pm window is the weakest at 45.9%, 48 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 August delays on Southwest Airlines at SEA?
August is the weakest month at 53.3% on time, compared with 87.7% in January. Across the year that is 34 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- Southwest Airlines network-wide record
- Seattle-Tacoma International (SEA) all carriers
- SEA to DEN route record67.3%
- SEA to SMF route record73.3%
- SEA to OAK route record69.8%
- SEA to PHX route record65.1%
- Seattle and Portland airports: why the evening flight holds up
- Why the first flight of the morning is statistically safest
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.