Airport month record

SEAAUG

Seattle-Tacoma International in August 2025

Departures: 15,970
Month: August 2025
National, same month: 77.4%
Carriers: 10

Historical statistics for August 2025, not live status or a forecast for this year’s August. For today’s conditions at SEA, see live FAA status.

SEA in August sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, 4 points worse than the national rate of 77.4%. The late ones land roughly 50 minutes behind schedule. That rests on 15,970 flights, of which SkyWest Airlines flew 2,757 at 86.3% on time.

SkyWest Airlines is the most reliable of the six carriers covered here at 86.3% on time across 2,757 flights.

On time

73.6%

Arrivals under 15 minutes late, of 15,813 completed departures

Avg delay

51 min

Across delayed arrivals only, not all flights

Cancelled

0.66%

Nationally in August: 1.08%

Whole year

79.4%

SEA across all twelve months

These figures cover 15,970 departures from Seattle-Tacoma International in August 2025. On time means an arrival less than 15 minutes after the scheduled gate time, the DOT's threshold, and the national comparison uses every US departure in the same month rather than the whole year.

Against the year

August next to SEA's other months

Against SEA's own year, August ran 6 points worse than the twelve-month rate of 79.4%, which makes it number eleven of twelve months, best first. Either side of it, July ran 69.2% on time and September 82.9%, so a trip moved by a few weeks would have landed in a better stretch.

SEA month by month
Month	Flights	On time	Avg delay	Cancelled	Grade
July 2025	16,577	69.2%	57 min	1.38%	C
August 2025 (this page)	15,970	73.6%	51 min	0.66%	C+
September 2025	14,552	82.9%	50 min	0.29%	B+
October 2025	13,859	82.9%	58 min	1.16%	B
November 2025	12,616	81.9%	58 min	1.69%	B
December 2025	13,023	74.0%	59 min	1.02%	C
January 2026	11,927	81.6%	60 min	1.91%	B
February 2026	11,000	84.4%	56 min	0.78%	B+
March 2026	12,830	80.2%	64 min	2.23%	B
April 2026	12,864	85.6%	56 min	0.17%	A+
May 2026	14,564	82.2%	52 min	0.41%	B+
June 2026	15,402	78.1%	57 min	0.48%	B+

Departure window

The best time of day to leave SEA in August

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 23 points, against 21 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,690 flights89.7%
8am–11am3,433 flights79.6%
11am–2pm3,019 flights66.8%
2pm–5pm2,407 flights70.0%
5pm–8pm2,340 flights69.3%
8pm–5am3,081 flights70.8%

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

The weak window here is the middle of the day, not the evening: 11am–2pm runs 66.8% on time against 89.7% for 5am–8am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 8am–11am window is the busiest, with 3,433 flights scheduled in it.

Across the week, Tuesday is the strongest day at 79.8% on time and Friday the weakest at 69.4%. 10 points is a smaller lever than departure hour, but it is free.

Carrier by carrier

Which airlines ran best at SEA in August

The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 86.3% of the time; Southwest Airlines manages 64.9%. Sample sizes sit next to every figure, because a two-point gap across 898 flights means less than a ten-point one.

Carriers at SEA in August 2025
Airline	Flights	On time	Avg delay	Cancelled	Grade
Alaska Airlines	7,258	67.1%	44 min	0.94%	C+
Delta Air Lines	2,919	81.5%	58 min	0.34%	B+
SkyWest Airlines	2,757	86.3%	46 min	0.04%	A+
United Airlines	972	75.0%	80 min	0.72%	B+
Southwest Airlines	898	64.9%	45 min	0.00%	D+
American Airlines	626	71.4%	85 min	2.72%	C
Hawaiian Airlinesthin sample	205	55.9%	67 min	0.49%	D+
Frontier Airlinesthin sample	162	72.5%	92 min	1.23%	C
JetBlue Airwaysthin sample	93	66.3%	108 min	0.00%	C+
Envoy Airthin sample	68	87.9%	52 min	0.00%	A+

The spread between SkyWest and Southwest is 21 points, wide enough that it should decide the booking. On a hundred trips that is 21 more arrivals inside the on-time window.

Route by route

Busiest routes out of SEA in August

Routes from SEA in August 2025
Route	Flights	On time	Avg delay	Cancelled	Grade
SEA to ANC · Anchorage	724	72.3%	46 min	1.10%	C
SEA to DEN · Denver	644	65.9%	55 min	0.78%	C+
SEA to LAX · Los Angeles	635	80.2%	51 min	0.47%	B+
SEA to SFO · San Francisco	619	73.9%	63 min	0.65%	C+
SEA to ORD · Chicago	599	60.9%	71 min	1.67%	D
SEA to PHX · Phoenix	585	75.7%	55 min	0.34%	B+
SEA to GEG · Spokane	513	74.3%	43 min	0.58%	C+
SEA to LAS · Las Vegas	487	74.7%	45 min	0.00%	C+
SEA to DFW · Dallas-Fort Worth	476	72.6%	73 min	2.73%	C
SEA to SMF · Sacramento	427	77.5%	44 min	0.23%	B+
SEA to SAN · San Diego	426	72.3%	44 min	1.64%	C
SEA to PDX · Portland	416	81.7%	47 min	0.00%	B+
SEA to SLC · Salt Lake City	408	77.5%	49 min	0.98%	B+
SEA to SJC · San Jose	395	78.8%	48 min	0.76%	B+
SEA to BOI · Boise	370	80.0%	40 min	0.00%	B+
SEA to SNA · Santa Anathin sample	359	80.7%	43 min	0.28%	B+
SEA to ATL · Atlantathin sample	316	79.6%	51 min	0.32%	B+
SEA to MSP · Minneapolisthin sample	291	77.2%	45 min	0.34%	B+
SEA to JFK · New Yorkthin sample	278	65.3%	58 min	0.72%	C+
SEA to BOS · Bostonthin sample	270	64.9%	60 min	0.00%	D+
SEA to ONT · Ontariothin sample	266	77.7%	39 min	0.38%	B+
SEA to HNL · Honoluluthin sample	248	57.9%	62 min	0.40%	D+
SEA to FAI · Fairbanksthin sample	246	73.0%	52 min	0.81%	C+
SEA to EWR · Newarkthin sample	229	70.5%	80 min	0.87%	C+
SEA to IAH · Houstonthin sample	228	68.8%	49 min	1.32%	C

Delay causes

What held SEA up in August

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 215,000 reported delay minutes.

Carrier
42%
Late-arriving aircraft
36%
National Airspace System
20%
Extreme weather
2%
Security
0%

36% 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 215,000 reported delay minutes here, that single category outweighs weather by 20 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 214,964 reported delay minutes.

Cancellations are rare at 0.66%, below the national 1.08% 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.

6.1% of arrivals land an hour or more late, close to the national 8.2%. 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.

What to do with this

Flying from SEA in August

For a August trip through SEA: plan on this being one of the airport's harder months. The 5am–8am departures held up best at 89.7% on time, and with 6.1% of arrivals an hour or more late, a connection here deserves more slack than the same trip in April would.

Seattle-Tacoma International (SEA), the whole year
SEA in July69.2%
SEA in September82.9%
SEA in October82.9%
SEA in November81.9%
SEA in December74.0%
SEA in January81.6%
SEA in February84.4%
SEA in March80.2%
SEA in April85.6%
SEA in May82.2%
SEA in June78.1%

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