Carrier route record

DLSEA→PHL

Delta Air Lines · Seattle to Philadelphia

Flights: 114
Period: September 2025 to August 2026
Share of route: 8%
Carriers: 3

Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Delta Air Lines.

Delta on SEA to PHL lands a B+, 6 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 roughly 55 minutes on average. That rests on 114 flights. The strongest carrier on the route with a full sample, American Airlines, flew 660 at 84.6% on time.

Set against the rest of the country, Delta's SEA to PHL record is 6 points better than the US average of 77.3%. That gap is worth roughly 59 fewer late arrivals for every thousand flights.

On time

83.2%

Arrivals under 15 minutes late, of 113 completed flights

Avg delay

54 min

Across delayed arrivals only, not all flights

Cancelled

0.88%

National rate is 1.89%

Whole route

82.7%

Every carrier on SEA to PHL, 1,431 flights

These figures cover 114 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

Delta against every carrier on SEA to PHL

Delta flew 114 of the 1,431 flights on SEA to PHL, about 8% of it. Its 83.2% on time is about level with the route as a whole at 82.7%. Ranked by on-time rate it is number two of three carriers on the route, where the range runs from American at 84.6% to Alaska at 80.7%.

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.

On-time performance by carrier on SEA to PHL
Airline	Flights	On time	Avg delay	Cancelled	Grade
American Airlines	660	84.6%	104 min	2.12%	B
Delta Air Lines (this page)thin 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.

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Departure window

When Delta runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 19 points, against 4 points between the best and worst carrier.

5am–8am—
8am–11am31 flights96.8%
11am–2pm—
2pm–5pm—
5pm–8pm—
8pm–5am83 flights78.0%

Scale runs 70% to 100%. Rows with fewer than 30 flights show a dash.

Book the morning departure. Flights leaving between 8am–11am arrive on time 96.8% of the time, against 78.0% for the overnight window. That is 19 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 83 flights scheduled in it.

Across the year

Delta on SEA to PHL through the year

Apr–Jun 202651 flights84.3%
Jul–Sep 202663 flights82.3%

Scale runs 75% to 90%.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 83.2% on time across 114 flights.

Split by quarter, Delta on SEA to PHL logged 51 flights in Apr–Jun 2026 and 63 flights in Jul–Sep 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 83.2% annual figure is the one to use.

Arrival by arrival

How late Delta on SEA to PHL runs when it is late

Delta on SEA to PHL often beats the schedule: 43 of 113 completed flights, 38%, arrived 15 minutes or more early. The 19 late arrivals split 4 under half an hour, 12 between 30 and 60 minutes, and 3 an hour or more.

15+ min early43 flights38.1%
Within 15 min51 flights45.1%
15–29 min late4 flights3.5%
30–59 min late12 flights10.6%
1–2 hours late2 flights1.8%
2+ hours late1 flights0.9%

Scale runs 0% to 100%.

Share of 113 completed flights by arrival against schedule.

A late pushback is often recovered here: of 20 departures that left 15 minutes late or more, 6 still arrived on time. 5 flights left on time and still arrived late.

The worst days

Worst days for Delta on SEA to PHL

The latest arrival of the period was on 20 August 2026, 4 hours 2 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. Three of the five worst days fell in July 2026.

The latest arrivals of Delta on SEA to PHL in the period
Date	Arrived late by	Largest filed cause
20 August 2026	4 hours 2 minutes	Late-arriving aircraft
15 June 2026	1 hour 18 minutes	Late-arriving aircraft
17 July 2026	1 hour 10 minutes	Carrier
19 July 2026	58 minutes	National Airspace System
6 July 2026	55 minutes	Late-arriving aircraft

Delay causes

Why Delta runs late on this route

Late-arriving aircraft accounts for 53% of the 1,020 delay minutes carriers reported here, and the remaining four split what is left.

Late-arriving aircraft
53%
National Airspace System
25%
Carrier
22%

53% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 1,020 reported delay minutes here, that single category outweighs weather by 53 to one. The split is drawn from 1,020 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 96.8% on time here.

Cancellations are rare at 0.88%, 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 costs

Badly late arrivals are rare here: only 2.7% land an hour or more behind schedule, against 8.3% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

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 113 flights, 14 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 14 points of difference.

One caution: this is a thin sample. 114 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.

What to do with this

Booking Delta on SEA to PHL

Put together: treat all of this as provisional. 114 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 83.2% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 113 completed flights over 12 months sit behind that.

Where to go next

Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated 22 October 2026; recomputed monthly. How this data is collected.

Key figures