Carrier route record
ASMIA→SEA
Alaska Airlines · Miami to Seattle
- Flights
- 392
- Period
- July 2025 to June 2026
- Share of route
- 33%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Alaska Airlines.
Alaska on MIA to SEA draws a C. About one flight in three arrives at least 15 minutes late, and the typical late arrival is about 50 minutes behind schedule. Build slack into anything you connect to. That rests on 392 flights. The strongest carrier on the route with a full sample, American Airlines, flew 423 at 69.5% on time.
The national on-time rate over the same period is 77.6%, so Alaska on MIA to SEA runs 12 points behind the country as a whole. Across a thousand flights that is about 122 extra late arrivals.
Key figures
On time
65.4%
Arrivals under 15 minutes late, of 384 completed flights
Avg delay
50 min
Across delayed arrivals only, not all flights
Cancelled
1.53%
National rate is 1.81%
Whole route
65.7%
Every carrier on MIA to SEA, 1,180 flights
These figures cover 392 flights between July 2025 and June 2026. Beyond the headline rate, 9.1% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Carrier by carrier
Alaska against every carrier on MIA to SEA
Alaska flew 392 of the 1,180 flights on MIA to SEA, about 33% of it. Its 65.4% on time is about level with the route as a whole at 65.7%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from American at 69.5% to Delta at 61.6%.
The choice of carrier is not cosmetic here. American Airlines arrives on time 69.5% of the time; Delta Air Lines manages 61.6%. Sample sizes sit next to every figure, because a two-point gap across 365 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 423 | 69.5% | 56 min | 0.47% | C+ |
| Alaska Airlines (this page) | 392 | 65.4% | 50 min | 1.53% | C |
| Delta Air Lines | 365 | 61.6% | 93 min | 1.64% | D |
American leads Delta by 8 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
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 flights64.7%
- 8pm–5am—
Scale runs 55% to 80%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 64.7% on time, against 73.3% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. 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 43.3% on time, 40 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, Monday is the strongest day at 75.5% on time and Thursday the weakest at 55.6%. 20 points is a smaller lever than departure hour, but it is free.
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 6,673 reported delay minutes.
- 34%Late-arriving aircraft
- 32%Carrier
- 28%National Airspace System
- 5%Extreme weather
- 1%Security
34% 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 6,673 reported delay minutes here, that single category outweighs weather by 7 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 6,673 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 1.53% against a national 1.81%, which is ordinary. Diversions add another 0.51%.
Connections and stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.1% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
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 78.8% on time across 391 flights, 13 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 13 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 65.4% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 384 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 SEA69.5%
- Delta Air Lines on MIA to SEA61.6%
- 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
- How often a connection fails at the major US hubs
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.