Route reliability record
DEN→PHL
Denver to Philadelphia
- Flights
- 3,003
- Period
- July 2025 to June 2026
- Distance
- 1,558 mi
- Carriers
- 4
This route sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 5 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 3,003 flights, of which United Airlines flew 952 at 79.9% on time.
United Airlines is the most reliable of the three carriers covered here at 79.9% on time across 952 flights.
Key figures
On time
73.1%
Arrivals under 15 minutes late, of 2,962 completed flights
Avg delay
76 min
Across delayed arrivals only, not all flights
Cancelled
1.17%
National rate is 1.81%
Best carrier
United
79.9% on time across 952 flights
These figures cover 3,003 flights between July 2025 and June 2026. Beyond the headline rate, 9.5% 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 DEN to PHL
The choice of carrier is not cosmetic here. United Airlines arrives on time 79.9% of the time; Southwest Airlines manages 63.7%. Sample sizes sit next to every figure, because a two-point gap across 879 flights means less than a ten-point one.
| 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 | 879 | 63.7% | 58 min | 0.91% | D+ |
| Frontier Airlinesthin sample | 295 | 62.3% | 103 min | 2.03% | D |
The spread between United and Southwest is 16 points, wide enough that it should decide the booking. On a hundred trips that is 16 more arrivals inside the on-time window.
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 30 points, against 16 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am209 flights88.7%
- 8am–11am784 flights82.8%
- 11am–2pm547 flights75.8%
- 2pm–5pm398 flights69.1%
- 5pm–8pm692 flights59.2%
- 8pm–5am373 flights69.9%
Scale runs 50% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 59.2% on time, against 88.7% 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.
Across the year
When delays peak on this route
This route's year swings by 21 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 63.1% on time, 21 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 317 flights.
Across the week, Tuesday is the strongest day at 81.6% on time and Thursday the weakest at 67.9%. 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. Late-arriving aircraft accounts for 43% of the 61,000 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.
- 43%Late-arriving aircraft
- 40%Carrier
- 16%National Airspace System
- 1%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. That is a cascade, and cascades start small and grow through the day. Across 61,000 reported delay minutes here, that single category outweighs weather by 30 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 60,618 reported delay minutes.
The largest share of delay minutes, 40%, 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 24,000 of the 61,000 delay minutes reported here.
Cancellations sit at 1.17% against a national 1.81%, which is ordinary. Diversions add another 0.20%.
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. 9.5% 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 runs 74.9% on time across 3,005 flights, within 2 points 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 3,003 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.
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 July 63.1%, a swing of 21 points. If the dates move at all, move them out of July before you think about anything else. 2,962 completed flights over 12 months sit behind that.
Common questions
DEN to PHL questions
How often is DEN to PHL delayed?
About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 26.9% of the 3,003 flights in this analysis, against 22.4% 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 79.9% on time across 952 flights. Southwest Airlines is at the other end on 63.7%, a gap of 16 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 88.7% on time. The 5pm–8pm window is the weakest at 59.2%, 30 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 DEN to PHL?
July is the weakest month at 63.1% on time, compared with 84.5% in November. Across the year that is 21 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-time record79.9%
- American Airlines on-time record78.8%
- Southwest Airlines on-time record63.7%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.