Route reliability record
MIA→SEA
Miami to Seattle
- Flights
- 1,180
- Period
- July 2025 to June 2026
- Distance
- 2,724 mi
- Carriers
- 3
This route draws a C. About one flight in three arrives at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 1,180 MIA to SEA flights, of which American Airlines flew 423 at 69.5% on time.
Best time to fly MIA to SEA: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 80.4% of the time and Tuesday flights 73.8%, against 65.7% for the route overall.
American Airlines is the most reliable of the three carriers covered here at 69.5% on time across 423 flights.
Key figures
On time
65.7%
Arrivals under 15 minutes late, of 1,161 completed flights
Avg delay
67 min
Across delayed arrivals only, not all flights
Cancelled
1.19%
National rate is 1.81%
Best carrier
American
69.5% on time across 423 flights
These figures cover 1,180 flights between July 2025 and June 2026. Beyond the headline rate, 10.8% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
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 69.5% of the time; Delta Air Lines manages 61.6%. Sample sizes sit next to every figure, because a two-point gap across 365 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 423 | 69.5% | 56 min | 0.47% | C+ |
| Alaska Airlines | 392 | 65.4% | 50 min | 1.53% | C |
| Delta Air Lines | 365 | 61.6% | 93 min | 1.64% | D |
American leads Delta by 8 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.
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 | 69.2% | 69.5% | 0.47% | 8am–11am, Tue | — |
| 2. FLL → SEAFort Lauderdale to Seattle | Alaska Airlines | 65.6% | 66.5% | 1.30% | 5am–8am, Tue | AS 517 17:52 |
| 3. MIA → SEAMiami to Seattle | Alaska Airlines | 64.4% | 65.4% | 1.53% | 5am–8am, Mon | AS 305 18:20 |
| 4. MIA → SEAMiami to Seattle | Delta Air Lines | 60.6% | 61.6% | 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 18 points, against 8 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am51 flights80.4%
- 8am–11am61 flights80.3%
- 11am–2pm—
- 2pm–5pm4 flights—
- 5pm–8pm854 flights62.9%
- 8pm–5am210 flights68.9%
Scale runs 55% to 85%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 62.9% on time, against 80.4% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5pm–8pm window is the busiest, with 854 flights scheduled in it.
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. December was the busiest month here, with 121 flights.
Across the week, Tuesday is the strongest day at 73.8% on time and Sunday the weakest at 59.9%. 14 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 45% of the 27,000 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.
- 45%Carrier
- 31%Late-arriving aircraft
- 19%National Airspace System
- 4%Extreme weather
- 1%Security
The largest share of delay minutes, 45%, 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 12,000 of the 27,000 delay minutes reported here. The split is drawn from 26,536 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 80.4% on time here.
Cancellations sit at 1.19% against a national 1.81%, which is ordinary. Diversions add another 0.42%.
Connections and stage length
What a delay here actually costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 10.8% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum 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 77.3% on time across 1,179 flights, 12 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 12 points of difference.
The sample behind these figures is 1,180 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. 1,161 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 34.3% of the 1,180 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on MIA to SEA?
American Airlines leads at 69.5% on time across 423 flights. Delta Air Lines is at the other end on 61.6%, a gap of 8 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 5am–8am departure window is the strongest at 80.4% on time. The 5pm–8pm window is the weakest at 62.9%, 18 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 SEA69.5%
- Alaska Airlines on MIA to SEA65.4%
- Delta Air Lines on MIA to SEA61.6%
- MIA to ATL, a related route73.7%
- LAX to SEA, a related route85.4%
- MIA to LGA, a related route68.0%
- American Airlines on-time record69.5%
- Alaska Airlines on-time record65.4%
- Delta Air Lines on-time record61.6%
- How often a connection fails at the major US hubs
- The best time of day to fly, according to 7.04 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.