Carrier route record
ASMIA→SEA
Alaska Airlines · Miami to Seattle
- Flights
- 392
- Period
- September 2025 to August 2026
- Share of route
- 32%
- Carriers
- 3
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Alaska Airlines.
Alaska on MIA to SEA 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 77.3%. The late ones land roughly 50 minutes behind schedule. That rests on 392 flights. The strongest carrier on the route with a full sample, American Airlines, flew 475 at 72.5% on time.
The national on-time rate over the same period is 77.3%, so Alaska on MIA to SEA runs 8 points behind the country as a whole. Across a thousand flights that is about 82 extra late arrivals.
Key figures
On time
69.1%
Arrivals under 15 minutes late, of 385 completed flights
Avg delay
48 min
Across delayed arrivals only, not all flights
Cancelled
1.28%
National rate is 1.89%
Whole route
68.7%
Every carrier on MIA to SEA, 1,233 flights
These figures cover 392 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.
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Carrier by carrier
Alaska against every carrier on MIA to SEA
Alaska flew 392 of the 1,233 flights on MIA to SEA, about 32% of it. Its 69.1% on time is about level with the route as a whole at 68.7%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from American at 72.5% to Delta at 63.4%.
The choice of carrier is not cosmetic here. American Airlines arrives on time 72.5% of the time; Delta Air Lines manages 63.4%. Sample sizes sit next to every figure, because a two-point gap across 366 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 475 | 72.5% | 52 min | 0.42% | C+ |
| Alaska Airlines (this page) | 392 | 69.1% | 48 min | 1.28% | C |
| Delta Air Lines | 366 | 63.4% | 90 min | 1.64% | D |
American leads Delta by 9 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Alaska flight numbers on MIA to SEA
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Departure window
When Alaska runs best on this route
Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 392 flights.
- 5am–8am30 flights73.3%
- 8am–11am—
- 11am–2pm—
- 2pm–5pm—
- 5pm–8pm362 flights68.7%
- 8pm–5am—
Scale runs 60% to 80%. Rows with fewer than 30 flights show a dash.
The early departures do better, though not dramatically: 73.3% on time for the 5am–8am window against 68.7% for 5pm–8pm. Worth taking if the schedule allows, not worth an extra connection. The 5pm–8pm window is the busiest, with 362 flights scheduled in it.
Across the year
Alaska on MIA to SEA through the year
August is the worst month at 63.3% on time, 20 points below June, the best at 83.3%. 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. December was the busiest month here, with 46 flights.
Across the week, Tuesday is the strongest day at 75.9% on time and Friday the weakest at 62.5%, a spread of 13 points.
Arrival by arrival
How late Alaska on MIA to SEA runs when it is late
Alaska on MIA to SEA often beats the schedule: 107 of 385 completed flights, 28%, arrived 15 minutes or more early. The 119 late arrivals split 52 under half an hour, 39 between 30 and 60 minutes, and 28 an hour or more.
- 15+ min early107 flights27.8%
- Within 15 min159 flights41.3%
- 15–29 min late52 flights13.5%
- 30–59 min late39 flights10.1%
- 1–2 hours late17 flights4.4%
- 2+ hours late11 flights2.9%
Scale runs 0% to 100%.
Share of 385 completed flights by arrival against schedule.
26 of 105 late departures made up the time and arrived on time, 25% of them. In the other direction, 40 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at SEA.
The worst days
Worst days for Alaska on MIA to SEA
The latest arrival of the period was on 11 October 2025, 3 hours 5 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The five worst days are spread across October, December, April, August and March, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 11 October 2025 | 3 hours 5 minutes | Carrier |
| 14 December 2025 | 3 hours 2 minutes | Late-arriving aircraft |
| 26 April 2026 | 3 hours 2 minutes | Extreme weather |
| 30 August 2026 | 2 hours 54 minutes | Late-arriving aircraft |
| 5 March 2026 | 2 hours 25 minutes | Carrier |
Delay causes
Why Alaska runs late on this route
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 5,711 reported delay minutes.
- 36%Late-arriving aircraft
- 29%National Airspace System
- 28%Carrier
- 6%Extreme weather
- 1%Security
36% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 5,711 reported delay minutes here, that single category outweighs weather by 6 to one. The split is drawn from 5,711 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 73.3% on time here.
Cancellations sit at 1.28% against a national 1.89%, which is ordinary. Diversions add another 0.51%.
Connections and stage length
What a delay here costs
7.3% 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 roughly 50 minutes, which a normal layover absorbs.
At 2,724 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.
The return leg is a different operation and performs like one: it runs 80.5% on time across 391 flights, 11 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 11 points of difference.
One caution: this is a thin sample. 392 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Alaska on MIA to SEA
Put together: treat all of this as provisional. 392 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 69.1% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 385 completed flights over 12 months sit behind that.
Related
Where to go next
- MIA to SEA, every carrier
- Alaska on SEA to MIA, the return leg
- American Airlines on MIA to SEA72.5%
- Delta Air Lines on MIA to SEA63.4%
- Alaska Airlines network-wide record
- Miami International (MIA) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Why the first flight of the morning is statistically safest
- Worst months to fly in the US, ranked by the data
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.