Airport month record

SEADEC

Seattle-Tacoma International in December 2025

Departures: 13,023
Month: December 2025
National, same month: 73.2%
Carriers: 9

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

SEA in December sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, about a point better than the national rate of 73.2%. The late ones land about an hour behind schedule. That rests on 13,023 flights, of which SkyWest Airlines flew 2,271 at 82.2% on time.

SkyWest Airlines is the most reliable of the six carriers covered here at 82.2% on time across 2,271 flights.

On time

74.0%

Arrivals under 15 minutes late, of 12,857 completed departures

Avg delay

59 min

Across delayed arrivals only, not all flights

Cancelled

1.02%

Nationally in December: 1.55%

Whole year

79.4%

SEA across all twelve months

These figures cover 13,023 departures from Seattle-Tacoma International in December 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

December next to SEA's other months

Against SEA's own year, December ran 5 points worse than the twelve-month rate of 79.4%, which makes it number ten of twelve months, best first. Either side of it, November ran 81.9% on time and January 81.6%, 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	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 (this page)	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 December

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 14 points, against 11 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,582 flights83.4%
8am–11am2,754 flights75.5%
11am–2pm2,527 flights69.2%
2pm–5pm1,801 flights76.3%
5pm–8pm1,823 flights70.5%
8pm–5am2,536 flights72.4%

Scale runs 60% to 90%. 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 69.2% on time against 83.4% 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 2,754 flights scheduled in it.

Across the week, Tuesday is the strongest day at 81.3% on time and Friday the weakest at 67.1%. 14 points is a smaller lever than departure hour, but it is free.

Carrier by carrier

Which airlines ran best at SEA in December

The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 82.2% of the time; Alaska Airlines manages 70.9%. Sample sizes sit next to every figure, because a two-point gap across 6,123 flights means less than a ten-point one.

Carriers at SEA in December 2025
Airline	Flights	On time	Avg delay	Cancelled	Grade
Alaska Airlines	6,123	70.9%	48 min	0.83%	C+
Delta Air Lines	2,651	73.6%	74 min	2.34%	C
SkyWest Airlines	2,271	82.2%	69 min	0.26%	B+
United Airlines	608	80.3%	86 min	0.33%	B+
Southwest Airlines	543	72.3%	47 min	0.18%	C+
American Airlines	521	80.1%	67 min	0.58%	B+
Hawaiian Airlinesthin sample	151	57.8%	83 min	2.65%	D
Frontier Airlinesthin sample	117	59.3%	94 min	3.42%	D−
Envoy Airthin sample	38	73.7%	76 min	0.00%	C+

SkyWest leads Alaska by 11 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Route by route

Busiest routes out of SEA in December

Routes from SEA in December 2025
Route	Flights	On time	Avg delay	Cancelled	Grade
SEA to LAX · Los Angeles	632	73.8%	67 min	1.74%	C
SEA to PHX · Phoenix	628	72.2%	66 min	0.32%	C+
SEA to SFO · San Francisco	558	66.1%	65 min	0.72%	C+
SEA to ANC · Anchorage	478	54.6%	60 min	1.05%	F
SEA to LAS · Las Vegas	468	73.8%	49 min	0.43%	C+
SEA to DEN · Denver	468	80.5%	66 min	0.64%	B+
SEA to DFW · Dallas-Fort Worth	455	74.5%	59 min	0.66%	C+
SEA to GEG · Spokane	395	77.7%	66 min	0.76%	B+
SEA to ORD · Chicago	382	70.1%	71 min	1.83%	C
SEA to PDX · Portland	378	73.7%	54 min	0.53%	C+
SEA to SAN · San Diegothin sample	358	68.4%	50 min	1.96%	C
SEA to SJC · San Josethin sample	353	77.7%	44 min	0.85%	B+
SEA to SNA · Santa Anathin sample	319	78.7%	54 min	0.94%	B+
SEA to SLC · Salt Lake Citythin sample	305	76.6%	51 min	0.66%	B+
SEA to SMF · Sacramentothin sample	294	73.4%	57 min	0.34%	C+
SEA to ATL · Atlantathin sample	269	79.2%	68 min	1.49%	B
SEA to BOI · Boisethin sample	266	85.3%	53 min	0.00%	A+
SEA to HNL · Honoluluthin sample	256	60.6%	73 min	1.56%	D
SEA to JFK · New Yorkthin sample	232	72.1%	62 min	5.60%	C−
SEA to MSP · Minneapolisthin sample	208	81.1%	56 min	0.48%	B+
SEA to FAI · Fairbanksthin sample	201	54.8%	48 min	1.99%	F
SEA to ONT · Ontariothin sample	200	72.2%	51 min	1.00%	C
SEA to EWR · Newarkthin sample	179	80.3%	66 min	0.56%	B+
SEA to AUS · Austinthin sample	169	76.2%	63 min	0.59%	B+
SEA to IAH · Houstonthin sample	168	75.0%	50 min	0.00%	B+

Delay causes

What held SEA up in December

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 196,000 reported delay minutes.

Carrier
40%
Late-arriving aircraft
34%
National Airspace System
20%
Extreme weather
6%
Security
0%

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 79,000 of the 196,000 delay minutes reported here. The split is drawn from 196,341 reported delay minutes.

Cancellations sit at 1.02% against a national 1.55%, which is ordinary. Diversions add another 0.25%.

7.2% of arrivals land an hour or more late, close to the national 10.0%. 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 about an hour, which a normal layover absorbs.

What to do with this

Flying from SEA in December

For a December trip through SEA: plan on this being one of the airport's harder months. The 5am–8am departures held up best at 83.4% on time, and with 7.2% 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 August73.6%
SEA in September82.9%
SEA in October82.9%
SEA in November81.9%
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