Carrier route record
WNDEN→PHL
Southwest Airlines · Denver to Philadelphia
- Flights
- 879
- Period
- July 2025 to June 2026
- Share of route
- 29%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on DEN to PHL draws a D+. Roughly 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 879 flights. The strongest carrier on the route with a full sample, United Airlines, flew 952 at 79.9% on time.
The national on-time rate over the same period is 77.6%, so Southwest on DEN to PHL runs 14 points behind the country as a whole. Across a thousand flights that is about 139 extra late arrivals.
Key figures
On time
63.7%
Arrivals under 15 minutes late, of 870 completed flights
Avg delay
58 min
Across delayed arrivals only, not all flights
Cancelled
0.91%
National rate is 1.81%
Whole route
73.1%
Every carrier on DEN to PHL, 3,003 flights
These figures cover 879 flights between July 2025 and June 2026. Beyond the headline rate, 11.3% 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
Southwest against every carrier on DEN to PHL
Southwest flew 879 of the 3,003 flights on DEN to PHL, about 29% of it. Its 63.7% on time is 9 points worse than the route as a whole, which runs 73.1%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from United at 79.9% to Frontier at 62.3%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: about a point 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 |
|---|---|---|---|---|---|
| United Airlines | 952 | 79.9% | 66 min | 0.53% | B+ |
| American Airlines | 877 | 78.8% | 103 min | 1.82% | B |
| Southwest Airlines (this page) | 879 | 63.7% | 58 min | 0.91% | D+ |
| Frontier Airlinesthin sample | 295 | 62.3% | 103 min | 2.03% | D |
No carrier stands out. United tops the table at 79.9%, about a point clear of the bottom, which is inside the range this kind of sample moves year to year.
Departure window
When Southwest runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 32 points, against about a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am—
- 8am–11am243 flights77.0%
- 11am–2pm221 flights73.9%
- 2pm–5pm96 flights67.4%
- 5pm–8pm309 flights44.7%
- 8pm–5am10 flights—
Scale runs 35% to 80%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 44.7% on time, against 77.0% for the 8am–11am 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 309 flights scheduled in it.
Across the year
Southwest on DEN to PHL through the year
Delays peak in May, when the on-time rate falls to 46.8%. January is the strongest month at 80.0%. Moving a flexible trip across that boundary buys 33 points. August was the busiest month here, with 91 flights.
Across the week, Tuesday is the strongest day at 75.2% on time and Monday the weakest at 56.8%. 18 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 51% of the 18,000 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.
- 51%Late-arriving aircraft
- 30%Carrier
- 18%National Airspace System
- 1%Extreme weather
51% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 18,000 reported delay minutes here, that single category outweighs weather by 51 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 18,258 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 77.0% on time here.
Cancellations sit at 0.91% against a national 1.81%, which is ordinary. Diversions add another 0.11%.
Connections and stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 11.3% 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 1,558 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 69.0% on time across 879 flights, 5 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 5 points of difference.
One caution: this is a thin sample. 879 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 Southwest on DEN to PHL
Put together: treat all of this as provisional. 879 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 63.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 870 completed flights over 12 months sit behind that.
Related
Where to go next
- DEN to PHL, every carrier
- Southwest on PHL to DEN, the return leg
- United Airlines on DEN to PHL79.9%
- American Airlines on DEN to PHL78.8%
- Frontier Airlines on DEN to PHL62.3%
- Southwest Airlines network-wide record
- Denver International (DEN) delay statistics
- Philadelphia International (PHL) delay statistics
- Why the first flight of the morning is statistically safest
- How often a connection fails at the major US hubs
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.