Carrier route record
ASSEA→MIA
Alaska Airlines · Seattle to Miami
- Flights
- 391
- 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 SEA to MIA lands a B+, about a point better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 40 minutes on average. That is a workable record, not a spotless one. That rests on 391 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 365 at 78.2% on time.
The US average over the same twelve months is 77.6%, so there is little to separate Alaska on SEA to MIA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
78.8%
Arrivals under 15 minutes late, of 386 completed flights
Avg delay
38 min
Across delayed arrivals only, not all flights
Cancelled
0.77%
National rate is 1.81%
Whole route
77.3%
Every carrier on SEA to MIA, 1,179 flights
These figures cover 391 flights between July 2025 and June 2026. The median arrival is 5 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Carrier by carrier
Alaska against every carrier on SEA to MIA
Alaska flew 391 of the 1,179 flights on SEA to MIA, about 33% of it. Its 78.8% on time is 2 points better than the route as a whole, which runs 77.3%. Ranked by on-time rate it is first of three carriers on the route, where the range runs from Alaska at 78.8% to American at 75.1%.
The two carriers here are closely matched: 3 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Alaska Airlines (this page) | 391 | 78.8% | 38 min | 0.77% | B+ |
| Delta Air Lines | 365 | 78.2% | 60 min | 1.37% | B |
| American Airlines | 423 | 75.1% | 58 min | 0.71% | B+ |
No carrier stands out. Delta tops the table at 78.2%, 3 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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 391 flights.
There are not enough flights in each departure window to split Alaska's SEA to MIA record by time of day without the percentages moving on noise. The headline rate of 78.8% is the reliable figure here.
Across the year
Alaska on SEA to MIA through the year
August is the worst month at 66.7% on time, 30 points below May, the best at 96.8%. 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 45 flights.
Across the week, Tuesday is the strongest day at 85.2% on time and Friday the weakest at 67.9%. 17 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Alaska runs late on this route
One category carries most of the weight here. National Airspace System accounts for 67% of the 3,110 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 67%National Airspace System
- 28%Carrier
- 4%Late-arriving aircraft
- 1%Extreme weather
67% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 2,097 minutes out of 3,110, against a national NAS share of 21%. The split is drawn from 3,110 reported delay minutes.
Cancellations are rare at 0.77%, 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.
Connections and stage length
What a delay here costs
Badly late arrivals are rare here: only 2.8% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
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 65.4% on time across 392 flights, 13 points below 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. 391 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 SEA to MIA
Put together: treat all of this as provisional. 391 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 78.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 386 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to MIA, every carrier
- Alaska on MIA to SEA, the return leg
- Delta Air Lines on SEA to MIA78.2%
- American Airlines on SEA to MIA75.1%
- Alaska Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Miami International (MIA) delay statistics
- Worst months to fly in the US, ranked by the data
- Late aircraft, weather, or the airline: what actually causes US flight delays
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.