Route reliability record
SEA→MIA
Seattle to Miami
- Flights
- 1,179
- Period
- July 2025 to June 2026
- Distance
- 2,724 mi
- Carriers
- 3
This route lands a B+, level with the national rate of 77.6%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by roughly 50 minutes on average. That is a workable record, not a spotless one. That rests on 1,179 SEA to MIA flights, of which Alaska Airlines flew 391 at 78.8% on time.
Best time to fly SEA to MIA: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 84.8% of the time and Wednesday flights 82.1%, against 77.3% for the route overall.
Alaska Airlines is the most reliable of the three carriers covered here at 78.8% on time across 391 flights.
Key figures
On time
77.3%
Arrivals under 15 minutes late, of 1,161 completed flights
Avg delay
52 min
Across delayed arrivals only, not all flights
Cancelled
0.93%
National rate is 1.81%
Best carrier
Alaska
78.8% on time across 391 flights
These figures cover 1,179 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
Which airline is most reliable on SEA to MIA
The three carriers here are closely matched: 4 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 | 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. Alaska tops the table at 78.8%, 4 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Flights on SEA to MIA
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
Best ways to make this trip
The most reliable ways to fly Seattle to Miami
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 1 of the top 4 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SEA → FLLSeattle to Fort Lauderdale | Alaska Airlines | 81.0% | 81.4% | 0.43% | 8am–11am, Wed | AS 516 07:55 |
| 2. SEA → MIASeattle to Miami | Alaska Airlines | 78.2% | 78.8% | 0.77% | 8am–11am, Tue | — |
| 3. SEA → MIASeattle to Miami | Delta Air Lines | 77.1% | 78.2% | 1.37% | 5am–8am, Tue | DL 506 08:00 |
| 4. SEA → MIASeattle to Miami | American Airlines | 74.6% | 75.1% | 0.71% | 11am–2pm, Thu | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
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 1,179 flights.
- 5am–8am66 flights84.8%
- 8am–11am664 flights78.1%
- 11am–2pm58 flights75.4%
- 2pm–5pm—
- 5pm–8pm—
- 8pm–5am391 flights74.9%
Scale runs 65% to 90%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 84.8% of the time, against 74.9% for the overnight window. That is 10 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 664 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 26 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
August is the worst month at 64.1% on time, 26 points below October, the best at 90.2%. 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. June was the busiest month here, with 120 flights.
Across the week, Wednesday is the strongest day at 82.1% on time and Friday the weakest at 68.7%. 13 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Carrier accounts for 43% of the 14,000 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.
- 43%Carrier
- 33%National Airspace System
- 22%Late-arriving aircraft
- 2%Extreme weather
The largest share of delay minutes, 43%, 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 5,954 of the 14,000 delay minutes reported here. The split is drawn from 13,804 reported delay minutes.
33% 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 4,543 minutes out of 14,000, against a national NAS share of 21%.
Cancellations sit at 0.93% against a national 1.81%, which is ordinary. Diversions add another 0.59%.
Connections and stage length
What a delay here actually costs
5.3% of arrivals land an hour or more late, close to the national 8.1%. 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 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 65.7% on time across 1,180 flights, 12 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 12 points of difference.
The sample behind these figures is 1,179 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in MIA after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. October runs 90.2% on time and August 64.1%, a swing of 26 points. If the dates move at all, move them out of August before you think about anything else. 1,161 completed flights over 12 months sit behind that.
Common questions
SEA to MIA questions
How often is SEA to MIA delayed?
Roughly one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.7% of the 1,179 flights in this analysis, against 22.4% nationally. Delayed flights are late by roughly 50 minutes on average.
Which airline is most reliable on SEA to MIA?
Alaska Airlines leads at 78.8% on time across 391 flights. American Airlines is at the other end on 75.1%, a gap of 4 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on SEA to MIA?
The 5am–8am departure window is the strongest at 84.8% on time. The 8pm–5am window is the weakest at 74.9%, 10 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are August delays on SEA to MIA?
August is the weakest month at 64.1% on time, compared with 90.2% in October. Across the year that is 26 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- MIA to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- Miami International (MIA) delay statistics
- Alaska Airlines on SEA to MIA78.8%
- Delta Air Lines on SEA to MIA78.2%
- American Airlines on SEA to MIA75.1%
- SEA to LAX, a related route83.4%
- ATL to MIA, a related route71.0%
- SEA to PHX, a related route79.2%
- Alaska Airlines on-time record78.8%
- Delta Air Lines on-time record78.2%
- American Airlines on-time record75.1%
- The best time of day to fly, according to 7.04 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. SEA to MIA and MIA to SEA are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.