Route reliability record
SEA→PHL
Seattle to Philadelphia
- Flights
- 1,431
- Period
- September 2025 to August 2026
- Distance
- 2,379 mi
- Carriers
- 3
This route lands a B, 5 points better than the national rate of 77.3%. About one flight in six arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That rests on 1,431 SEA to PHL flights, of which American Airlines flew 660 at 84.6% on time.
Best time to fly SEA to PHL: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 86.4% of the time and Tuesday flights 87.5%, against 82.7% for the route overall.
Set against the rest of the country, this route's record is 5 points better than the US average of 77.3%. That gap is worth roughly 54 fewer late arrivals for every thousand flights.
Key figures
On time
82.7%
Arrivals under 15 minutes late, of 1,401 completed flights
Avg delay
70 min
Across delayed arrivals only, not all flights
Cancelled
1.54%
National rate is 1.89%
Best carrier
American
84.6% on time across 660 flights
These figures cover 1,431 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
Which airline is most reliable on SEA to PHL
The two 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 |
|---|---|---|---|---|---|
| American Airlines | 660 | 84.6% | 104 min | 2.12% | B |
| Delta Air Linesthin sample | 114 | 83.2% | 54 min | 0.88% | B+ |
| Alaska Airlines | 657 | 80.7% | 46 min | 1.07% | B |
No carrier stands out. American tops the table at 84.6%, 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 PHL
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 Philadelphia
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SEA → PHLSeattle to Philadelphia | American Airlines | 82.8% | 84.6% | 2.12% | 5am–8am, Tue | — |
| 2. SEA → PHLSeattle to Philadelphia | Alaska Airlines | 79.8% | 80.7% | 1.07% | 8pm–5am, Tue | AS 442 08:28 |
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 1,431 flights.
- 5am–8am69 flights86.4%
- 8am–11am498 flights77.6%
- 11am–2pm162 flights82.6%
- 2pm–5pm—
- 5pm–8pm—
- 8pm–5am702 flights85.8%
Scale runs 70% to 90%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 86.4% of the time, against 77.6% for the morning window. That is 9 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8pm–5am window is the busiest, with 702 flights scheduled in it.
Explore
Filter SEA to PHL 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 PHL, the best departure window is 5am–8am at 86.4% on time and the worst is 8am–11am at 77.6%, a real gap of 8.8 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am86.4%
- 8–11am77.6%
- 11am–2pm82.6%
- 2–5pm—
- 5–8pm—
- 8pm–5am85.8%
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 18 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.
July is the worst month at 76.1% on time, 18 points below April, the best at 93.9%. 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. July was the busiest month here, with 185 flights.
Across the week, Tuesday is the strongest day at 87.5% on time and Thursday the weakest at 75.9%, a spread of 12 points.
Delay causes
Why this route gets delayed
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 17,000 reported delay minutes.
- 38%Carrier
- 37%Late-arriving aircraft
- 14%National Airspace System
- 10%Extreme weather
37% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 17,000 reported delay minutes here, that single category outweighs weather by 4 to one. The split is drawn from 17,066 reported delay minutes.
The largest share of delay minutes, 38%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 6,507 of the 17,000 delay minutes reported here.
Cancellations sit at 1.54% against a national 1.89%, which is ordinary. Diversions add another 0.56%.
Connections and stage length
What a delay here actually costs
5.0% 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 a little over an hour, which a normal layover absorbs.
At 2,379 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 69.4% on time across 1,431 flights, 13 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 13 points of difference.
The sample behind these figures is 1,431 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 PHL 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. April runs 93.9% on time and July 76.1%, a swing of 18 points. If the dates move at all, move them out of July before you think about anything else. 1,401 completed flights over 12 months sit behind that.
Common questions
SEA to PHL questions
How often is SEA to PHL delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 17.3% of the 1,431 flights in this analysis, against 22.7% nationally. Delayed flights are late by a little over an hour on average.
Which airline is most reliable on SEA to PHL?
American Airlines leads at 84.6% on time across 660 flights. Alaska Airlines is at the other end on 80.7%, 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 PHL?
The 5am–8am departure window is the strongest at 86.4% on time. The 8am–11am window is the weakest at 77.6%, 9 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 July delays on SEA to PHL?
July is the weakest month at 76.1% on time, compared with 93.9% in April. Across the year that is 18 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
- PHL to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- Philadelphia International (PHL) delay statistics
- American Airlines on SEA to PHL84.6%
- Delta Air Lines on SEA to PHL83.2%
- Alaska Airlines on SEA to PHL80.7%
- SEA to LAX, a related route82.0%
- ATL to PHL, a related route74.6%
- SEA to PHX, a related route78.2%
- American Airlines on-time record84.6%
- Delta Air Lines on-time record83.2%
- Alaska Airlines on-time record80.7%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. SEA to PHL and PHL 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.