Carrier route record
ASSEA→MIA
Alaska Airlines · Seattle to Miami
- Flights
- 391
- 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 SEA to MIA lands a B+, 3 points better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about 40 minutes on average. That rests on 391 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 365 at 80.7% on time.
The US average over the same twelve months is 77.3%, 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
80.5%
Arrivals under 15 minutes late, of 389 completed flights
Avg delay
40 min
Across delayed arrivals only, not all flights
Cancelled
0.26%
National rate is 1.89%
Whole route
79.7%
Every carrier on SEA to MIA, 1,231 flights
These figures cover 391 flights between September 2025 and August 2026. The median arrival is 9 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.
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Carrier by carrier
Alaska against every carrier on SEA to MIA
Alaska flew 391 of the 1,231 flights on SEA to MIA, about 32% of it. Its 80.5% on time is about level with the route as a whole at 79.7%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from Delta at 80.7% to American at 78.4%.
The two carriers here are closely matched: 2 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 |
|---|---|---|---|---|---|
| Delta Air Lines | 365 | 80.7% | 65 min | 1.37% | B |
| Alaska Airlines (this page) | 391 | 80.5% | 40 min | 0.26% | B+ |
| American Airlines | 475 | 78.4% | 68 min | 0.84% | B+ |
No carrier stands out. Delta tops the table at 80.7%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Alaska flight numbers on SEA to MIA
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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 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 80.5% is the reliable figure here.
Across the year
Alaska on SEA to MIA through the year
May is the best month on the calendar at 96.8% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. December was the busiest month here, with 45 flights.
Across the week, Tuesday is the strongest day at 90.7% on time and Friday the weakest at 69.6%, a spread of 21 points.
Arrival by arrival
How late Alaska on SEA to MIA runs when it is late
Alaska on SEA to MIA often beats the schedule: 150 of 389 completed flights, 39%, arrived 15 minutes or more early. Most of the lateness is short. 40 of the 76 late arrivals were under half an hour behind, and 13 reached an hour or more.
- 15+ min early150 flights38.6%
- Within 15 min163 flights41.9%
- 15–29 min late40 flights10.3%
- 30–59 min late23 flights5.9%
- 1–2 hours late11 flights2.8%
- 2+ hours late2 flights0.5%
Scale runs 0% to 100%.
Share of 389 completed flights by arrival against schedule.
14 of 47 late departures made up the time and arrived on time, 30% of them. In the other direction, 43 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 MIA.
The worst days
Worst days for Alaska on SEA to MIA
The latest arrival of the period was on 30 August 2026, 3 hours 34 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 30 August 2026 | 3 hours 34 minutes | Carrier |
| 14 December 2025 | 3 hours 19 minutes | Carrier |
| 7 March 2026 | 1 hour 52 minutes | National Airspace System |
| 27 December 2025 | 1 hour 48 minutes | Carrier |
| 5 March 2026 | 1 hour 30 minutes | National Airspace System |
Delay causes
Why Alaska runs late on this route
National Airspace System accounts for 58% of the 3,065 delay minutes carriers reported here, and the remaining four split what is left.
- 58%National Airspace System
- 36%Carrier
- 5%Late-arriving aircraft
- 1%Extreme weather
58% 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 1,780 minutes out of 3,065, against a national NAS share of 21%. The split is drawn from 3,065 reported delay minutes.
The largest share of delay minutes, 36%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 1,112 of the 3,065 delay minutes reported here.
Cancellations are rare at 0.26%, below the national 1.89% 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 3.3% land an hour or more behind schedule, against 8.3% 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 69.1% on time across 392 flights, 11 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 11 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 80.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 389 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 MIA80.7%
- American Airlines on SEA to MIA78.4%
- 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.