Carrier performance at one airport
WN→SEA
Southwest Airlines at Seattle-Tacoma International
- Departures
- 8,105
- Period
- July 2025 to June 2026
- Routes
- 13
- 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, 8 points worse than the national rate of 77.6%. The late ones land roughly 50 minutes behind schedule. That rests on 8,105 flights, of which Envoy Air flew 691 at 86.9% on time.
Measured against the airport rather than the country, Southwest Airlines runs 9 points behind the 79.4% 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
70.0%
8,047 completed departures
Avg delay
48 min
Across delayed flights only
Cancelled
0.41%
At SEA, this carrier only
Rank here
#8
Of 10 carriers clearing the floor at SEA
These figures cover 8,105 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.
Against the competition
Every carrier at SEA, ranked
The choice of carrier is not cosmetic here. Envoy Air arrives on time 86.9% of the time; JetBlue Airways manages 59.6%. 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 | 691 | 86.9% | 71 min | 0.00% | A+ |
| SkyWest Airlines | 29,109 | 86.1% | 58 min | 0.71% | A+ |
| Delta Air Lines | 32,257 | 81.5% | 65 min | 1.05% | B |
| United Airlines | 8,804 | 80.2% | 76 min | 0.80% | B+ |
| American Airlines | 6,630 | 79.2% | 97 min | 2.07% | B |
| Alaska Airlines | 76,697 | 77.2% | 47 min | 1.05% | B |
| Frontier Airlines | 1,401 | 73.6% | 90 min | 2.28% | C |
| Southwest Airlines (this page) | 8,105 | 70.0% | 48 min | 0.41% | C+ |
| Hawaiian Airlines | 1,034 | 60.5% | 82 min | 1.26% | D |
| JetBlue Airways | 413 | 59.6% | 109 min | 0.73% | D+ |
The spread between Envoy and JetBlue is 27 points, wide enough that it should decide the booking. On a hundred trips that is 27 more arrivals inside the on-time window.
Route by route
Where Southwest Airlines flies from SEA
Southwest Airlines operates 13 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 | 1,345 | 69.0% | 52 min | 0.59% | C+ |
| SEA to SMF · Sacramento | 1,156 | 71.9% | 48 min | 0.43% | C+ |
| SEA to OAK · Oakland | 1,127 | 71.6% | 54 min | 0.09% | C+ |
| SEA to PHX · Phoenix | 1,036 | 69.0% | 47 min | 0.68% | C+ |
| SEA to LAS · Las Vegas | 976 | 69.2% | 48 min | 0.51% | C+ |
| SEA to SJC · San Jose | 927 | 72.6% | 45 min | 0.32% | C+ |
| SEA to MDW · Chicago | 678 | 80.7% | 41 min | 0.59% | B+ |
| SEA to DAL · Dallasthin sample | 220 | 44.5% | 52 min | 0.00% | F+ |
| SEA to BNA · Nashvillethin sample | 125 | 64.8% | 39 min | 0.00% | D+ |
| SEA to BWI · Baltimorethin sample | 120 | 68.3% | 41 min | 0.00% | C+ |
| SEA to HOU · Houstonthin sample | 120 | 66.7% | 56 min | 0.00% | C+ |
| SEA to SAN · San Diegothin sample | 118 | 55.9% | 41 min | 0.00% | D+ |
| SEA to STL · St. Louisthin sample | 103 | 64.7% | 39 min | 0.00% | D+ |
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 43 points, against 27 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am2,052 flights94.1%
- 8am–11am1,335 flights83.6%
- 11am–2pm1,522 flights58.8%
- 2pm–5pm1,168 flights51.0%
- 5pm–8pm1,034 flights52.3%
- 8pm–5am994 flights60.3%
Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 94.1% of the time, against 51.0% for the afternoon window. That is 43 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 2,052 flights scheduled in it.
Across the year
Seasonal pattern
June is the worst month at 58.8% on time, 29 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. July was the busiest month here, with 988 flights.
Delay causes
What holds this operation up
- 53%Late-arriving aircraft
- 30%Carrier
- 15%National Airspace System
- 1%Extreme weather
- 1%Security
53% 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 117,000 reported delay minutes here, that single category outweighs weather by 53 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 116,631 reported delay minutes.
Cancellations are rare at 0.41%, 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.
6.6% 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 roughly 50 minutes kind, which a normal layover absorbs.
The sample behind these figures is 8,105 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 June 58.8%, a swing of 29 points. If the dates move at all, move them out of June before you think about anything else. 8,047 completed flights over 12 months sit behind that.
Common questions
Southwest Airlines at SEA
How often is Southwest Airlines at SEA delayed?
Roughly one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 30.0% of the 8,105 flights in this analysis, against 22.4% nationally. Delayed flights are late by roughly 50 minutes on average.
Which airline is most reliable on Southwest Airlines at SEA?
Envoy Air leads at 86.9% on time across 691 flights. JetBlue Airways is at the other end on 59.6%, a gap of 27 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 51.0%, 43 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 June delays on Southwest Airlines at SEA?
June is the weakest month at 58.8% on time, compared with 87.7% in January. Across the year that is 29 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
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.