Route reliability record
DEN→PHL
Denver to Philadelphia
- Flights
- 3,056
- Period
- September 2025 to August 2026
- Distance
- 1,558 mi
- Carriers
- 4
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, 5 points worse than the national rate of 77.3%. The late ones land a little over an hour behind schedule. That rests on 3,056 DEN to PHL flights, of which United Airlines flew 952 at 79.0% on time.
Best time to fly DEN to PHL: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 89.2% of the time and Tuesday flights 80.8%, against 72.8% for the route overall.
United Airlines is the most reliable of the three carriers covered here at 79.0% on time across 952 flights.
Key figures
On time
72.8%
Arrivals under 15 minutes late, of 3,007 completed flights
Avg delay
79 min
Across delayed arrivals only, not all flights
Cancelled
1.44%
National rate is 1.89%
Best carrier
United
79.0% on time across 952 flights
These figures cover 3,056 flights between September 2025 and August 2026. Beyond the headline rate, 10.2% 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 DEN to PHL
The choice of carrier is not cosmetic here. United Airlines arrives on time 79.0% of the time; Southwest Airlines manages 61.4%. Sample sizes sit next to every figure, because a two-point gap across 880 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 952 | 79.0% | 71 min | 0.53% | B+ |
| American Airlines | 925 | 78.7% | 113 min | 2.16% | B |
| Frontier Airlinesthin sample | 299 | 68.1% | 101 min | 3.68% | C− |
| Southwest Airlines | 880 | 61.4% | 59 min | 0.91% | D+ |
The spread between United and Southwest is 18 points, wide enough that it should decide the booking. On a hundred trips that is 18 more arrivals inside the on-time window.
Flight by flight
Flights on DEN 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 Denver 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. DEN → PHLDenver to Philadelphia | United Airlines | 78.6% | 79.0% | 0.53% | 8am–11am, Tue | UA 1575 09:35 |
| 2. DEN → PHLDenver to Philadelphia | American Airlines | 77.0% | 78.7% | 2.16% | 5am–8am, Fri | — |
| 3. DEN → PHLDenver to Philadelphia | Southwest Airlines | 60.8% | 61.4% | 0.91% | 8am–11am, Tue | — |
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 31 points, against 18 points between the best and worst carrier.
- 5am–8am256 flights89.2%
- 8am–11am784 flights84.1%
- 11am–2pm526 flights73.3%
- 2pm–5pm427 flights68.6%
- 5pm–8pm685 flights58.2%
- 8pm–5am378 flights68.4%
Scale runs 50% to 95%.
The 5pm–8pm window is where this operation falls apart: 58.2% on time, against 89.2% 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 8am–11am window is the busiest, with 784 flights scheduled in it.
Explore
Filter DEN 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 DEN to PHL, the best departure window is 5am–8am at 89.2% on time and the worst is 5pm–8pm at 58.2%, a wide gap of 31.0 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am89.2%
- 8–11am84.1%
- 11am–2pm73.3%
- 2–5pm68.6%
- 5–8pm58.2%
- 8pm–5am68.4%
best all US flightsScale 50% to 95%.
Across the year
When delays peak on this route
This route's year swings by 24 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.
August is the worst month at 60.7% on time, 24 points below November, the best at 84.5%. 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 344 flights.
Across the week, Tuesday is the strongest day at 80.8% on time and Monday the weakest at 66.3%, a spread of 15 points.
Delay causes
Why this route gets delayed
Late-arriving aircraft accounts for 43% of the 65,000 delay minutes carriers reported here, and the remaining four split what is left.
- 43%Late-arriving aircraft
- 37%Carrier
- 18%National Airspace System
- 2%Extreme weather
- 0%Security
43% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 65,000 reported delay minutes here, that single category outweighs weather by 22 to one. The split is drawn from 64,972 reported delay minutes.
The largest share of delay minutes, 37%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 24,000 of the 65,000 delay minutes reported here.
Cancellations sit at 1.44% against a national 1.89%, which is ordinary. Diversions add another 0.16%.
Connections and stage length
What a delay here actually costs
10.2% 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 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 runs 73.3% on time across 3,060 flights, within half a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
The sample behind these figures is 3,056 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. November runs 84.5% on time and August 60.7%, a swing of 24 points. If the dates move at all, move them out of August before you think about anything else. 3,007 completed flights over 12 months sit behind that.
Common questions
DEN to PHL questions
How often is DEN to PHL delayed?
Roughly one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 27.2% of the 3,056 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 DEN to PHL?
United Airlines leads at 79.0% on time across 952 flights. Southwest Airlines is at the other end on 61.4%, a gap of 18 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 DEN to PHL?
The 5am–8am departure window is the strongest at 89.2% on time. The 5pm–8pm window is the weakest at 58.2%, 31 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 August delays on DEN to PHL?
August is the weakest month at 60.7% on time, compared with 84.5% in November. Across the year that is 24 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 DEN — the return legseparate record
- Denver International (DEN) delay statistics
- Philadelphia International (PHL) delay statistics
- United Airlines on DEN to PHL79.0%
- American Airlines on DEN to PHL78.7%
- Frontier Airlines on DEN to PHL68.1%
- Southwest Airlines on DEN to PHL61.4%
- DEN to PHX, a related route75.6%
- ATL to PHL, a related route74.6%
- DEN to SLC, a related route78.2%
- United Airlines on-time record79.0%
- American Airlines on-time record78.7%
- Frontier Airlines on-time record68.1%
- Why the first flight of the morning is statistically safest
- Same route, different airline: where the carrier you pick matters most
Direction matters. DEN to PHL and PHL to DEN 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.