Route reliability record
SEA→MIA
Seattle to Miami
- Flights
- 1,231
- Period
- September 2025 to August 2026
- Distance
- 2,724 mi
- Carriers
- 3
This route lands a B+, 2 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 an hour on average. That rests on 1,231 SEA to MIA flights, of which Delta Air Lines flew 365 at 80.7% 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 84.8%, against 79.7% for the route overall.
Delta Air Lines is the most reliable of the three carriers covered here at 80.7% on time across 365 flights.
Key figures
On time
79.7%
Arrivals under 15 minutes late, of 1,214 completed flights
Avg delay
59 min
Across delayed arrivals only, not all flights
Cancelled
0.81%
National rate is 1.89%
Best carrier
Delta
80.7% on time across 365 flights
These figures cover 1,231 flights between September 2025 and August 2026. The median arrival is 8 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
Which airline is most reliable on SEA to MIA
The three 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 | 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
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.
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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 | 80.9% | 81.1% | 0.22% | 8am–11am, Wed | AS 516 08:23 |
| 2. SEA → MIASeattle to Miami | Alaska Airlines | 80.3% | 80.5% | 0.26% | 8am–11am, Tue | AS 305 08:12 |
| 3. SEA → MIASeattle to Miami | Delta Air Lines | 79.6% | 80.7% | 1.37% | 5am–8am, Wed | DL 506 08:00 |
| 4. SEA → MIASeattle to Miami | American Airlines | 77.7% | 78.4% | 0.84% | 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 1,231 flights.
- 5am–8am66 flights84.8%
- 8am–11am664 flights80.4%
- 11am–2pm110 flights81.5%
- 2pm–5pm—
- 5pm–8pm—
- 8pm–5am391 flights77.2%
Scale runs 70% to 90%. Rows with fewer than 30 flights show a dash.
The early departures do better, though not dramatically: 84.8% on time for the 5am–8am window against 77.2% for 8pm–5am. Worth taking if the schedule allows, not worth an extra connection. The 8am–11am window is the busiest, with 664 flights scheduled in it.
Explore
Filter SEA to MIA by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On SEA to MIA, the best departure window is 5am–8am at 84.8% on time and the worst is 8pm–5am at 77.2%, a real gap of 7.6 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am84.8%
- 8–11am80.4%
- 11am–2pm81.5%
- 2–5pm—
- 5–8pm—
- 8pm–5am77.2%
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 20 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.
October is the best month on the calendar at 90.2% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. July was the busiest month here, with 124 flights.
Across the week, Wednesday is the strongest day at 84.8% on time and Friday the weakest at 74.7%, a spread of 10 points.
Delay causes
Why this route gets delayed
Carrier accounts for 47% of the 14,000 delay minutes carriers reported here, and the remaining four split what is left.
- 47%Carrier
- 28%National Airspace System
- 23%Late-arriving aircraft
- 2%Extreme weather
The largest share of delay minutes, 47%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 6,751 of the 14,000 delay minutes reported here. The split is drawn from 14,429 reported delay minutes.
Cancellations are rare at 0.81%, 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 actually costs
5.1% 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 about an hour, 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 68.7% on time across 1,233 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.
The sample behind these figures is 1,231 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 March 70.3%, a swing of 20 points. If the dates move at all, move them out of March before you think about anything else. 1,214 completed flights over 12 months sit behind that.
Common questions
SEA to MIA questions
How often is SEA to MIA delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 20.3% of the 1,231 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SEA to MIA?
Delta Air Lines leads at 80.7% on time across 365 flights. American Airlines is at the other end on 78.4%, a gap of 2 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 77.2%, 8 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 March delays on SEA to MIA?
March is the weakest month at 70.3% on time, compared with 90.2% in October. Across the year that is 20 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
- Delta Air Lines on SEA to MIA80.7%
- Alaska Airlines on SEA to MIA80.5%
- American Airlines on SEA to MIA78.4%
- SEA to LAX, a related route82.0%
- ATL to MIA, a related route71.2%
- SEA to PHX, a related route78.2%
- Delta Air Lines on-time record80.7%
- Alaska Airlines on-time record80.5%
- American Airlines on-time record78.4%
- Worst months to fly in the US, ranked by the data
- Does flight distance affect delays? Less than it affects cancellations
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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.