Route reliability record
MIA→SEA
Miami to Seattle
- Flights
- 1,233
- Period
- September 2025 to August 2026
- Distance
- 2,724 mi
- Carriers
- 3
This route sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 9 points worse than the national rate of 77.3%. The late ones land about an hour behind schedule. That rests on 1,233 MIA to SEA flights, of which American Airlines flew 475 at 72.5% on time.
Best time to fly MIA to SEA: a 8am–11am departure, ideally on a Tuesday. Flights in that window arrived on time 88.9% of the time and Tuesday flights 76.7%, against 68.7% for the route overall.
American Airlines is the most reliable of the three carriers covered here at 72.5% on time across 475 flights.
Key figures
On time
68.7%
Arrivals under 15 minutes late, of 1,215 completed flights
Avg delay
64 min
Across delayed arrivals only, not all flights
Cancelled
1.05%
National rate is 1.89%
Best carrier
American
72.5% on time across 475 flights
These figures cover 1,233 flights between September 2025 and August 2026. Beyond the headline rate, 9.2% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Which airline is most reliable on MIA to SEA
The choice of carrier is not cosmetic here. American Airlines arrives on time 72.5% of the time; Delta Air Lines manages 63.4%. Sample sizes sit next to every figure, because a two-point gap across 366 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 475 | 72.5% | 52 min | 0.42% | C+ |
| Alaska Airlines | 392 | 69.1% | 48 min | 1.28% | C |
| Delta Air Lines | 366 | 63.4% | 90 min | 1.64% | D |
American leads Delta by 9 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Flights on MIA to SEA
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 Miami to Seattle
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. MIA → SEAMiami to Seattle | American Airlines | 72.2% | 72.5% | 0.42% | 8am–11am, Wed | — |
| 2. MIA → SEAMiami to Seattle | Alaska Airlines | 68.2% | 69.1% | 1.28% | 5am–8am, Tue | AS 305 18:20 |
| 3. FLL → SEAFort Lauderdale to Seattle | Alaska Airlines | 67.7% | 68.4% | 1.08% | 5pm–8pm, Thu | AS 517 18:30 |
| 4. MIA → SEAMiami to Seattle | Delta Air Lines | 62.4% | 63.4% | 1.64% | 5pm–8pm, Tue | DL 506 18:05 |
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 matters more here than the choice of carrier. The gap between the best and worst window is 24 points, against 9 points between the best and worst carrier.
- 5am–8am61 flights83.6%
- 8am–11am109 flights88.9%
- 11am–2pm—
- 2pm–5pm4 flights—
- 5pm–8pm849 flights65.1%
- 8pm–5am210 flights68.1%
Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 88.9% of the time, against 65.1% for the evening window. That is 24 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 849 flights scheduled in it.
Explore
Filter MIA to SEA 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 MIA to SEA, the best departure window is 8am–11am at 88.9% on time and the worst is 5pm–8pm at 65.1%, a wide gap of 23.8 points. All US flights leaving 8am–11am ran 83.9%.
- 5–8am83.6%
- 8–11am88.9%
- 11am–2pm—
- 2–5pm—
- 5–8pm65.1%
- 8pm–5am68.1%
best all US flightsScale 55% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 35 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.
Delays peak in March, when the on-time rate falls to 46.6%. June is the strongest month at 81.7%. Moving a flexible trip across that boundary buys 35 points. July was the busiest month here, with 125 flights.
Across the week, Tuesday is the strongest day at 76.7% on time and Sunday the weakest at 61.8%, a spread of 15 points.
Delay causes
Why this route gets delayed
Carrier accounts for 44% of the 24,000 delay minutes carriers reported here, and the remaining four split what is left.
- 44%Carrier
- 30%Late-arriving aircraft
- 21%National Airspace System
- 4%Extreme weather
- 1%Security
The largest share of delay minutes, 44%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 11,000 of the 24,000 delay minutes reported here. The split is drawn from 24,317 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 88.9% on time here.
Cancellations sit at 1.05% against a national 1.89%, which is ordinary. Diversions add another 0.41%.
Connections and stage length
What a delay here actually costs
9.2% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection 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 79.7% on time across 1,231 flights, 11 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 11 points of difference.
The sample behind these figures is 1,233 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 SEA 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. June runs 81.7% on time and March 46.6%, a swing of 35 points. If the dates move at all, move them out of March before you think about anything else. 1,215 completed flights over 12 months sit behind that.
Common questions
MIA to SEA questions
How often is MIA to SEA delayed?
About one flight in three arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 31.3% of the 1,233 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on MIA to SEA?
American Airlines leads at 72.5% on time across 475 flights. Delta Air Lines is at the other end on 63.4%, a gap of 9 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 MIA to SEA?
The 8am–11am departure window is the strongest at 88.9% on time. The 5pm–8pm window is the weakest at 65.1%, 24 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 MIA to SEA?
March is the weakest month at 46.6% on time, compared with 81.7% in June. Across the year that is 35 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
- SEA to MIA — the return legseparate record
- Miami International (MIA) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- American Airlines on MIA to SEA72.5%
- Alaska Airlines on MIA to SEA69.1%
- Delta Air Lines on MIA to SEA63.4%
- MIA to ATL, a related route74.2%
- LAX to SEA, a related route85.0%
- MIA to LGA, a related route67.4%
- American Airlines on-time record72.5%
- Alaska Airlines on-time record69.1%
- Delta Air Lines on-time record63.4%
- How often a connection fails at the major US hubs
- The best time of day to fly, according to 7.05 million flight records
Direction matters. MIA to SEA and SEA to MIA 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.