Route reliability record
STL→PHL
St. Louis to Philadelphia
- Flights
- 1,587
- Period
- July 2025 to June 2026
- Distance
- 814 mi
- Carriers
- 4
This route lands a B, 2 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 1,587 STL to PHL flights, of which American Airlines flew 630 at 81.3% on time.
Best time to fly STL to PHL: a 8am–11am departure, ideally on a Wednesday. Flights in that window arrived on time 89.9% of the time and Wednesday flights 84.5%, against 79.6% for the route overall.
The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
79.6%
Arrivals under 15 minutes late, of 1,561 completed flights
Avg delay
83 min
Across delayed arrivals only, not all flights
Cancelled
1.39%
National rate is 1.81%
Best carrier
American
81.3% on time across 630 flights
These figures cover 1,587 flights between July 2025 and June 2026. The median arrival is 7 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.
Carrier by carrier
Which airline is most reliable on STL to PHL
The two carriers here are closely matched: 5 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 |
|---|---|---|---|---|---|
| PSA Airlinesthin sample | 133 | 85.5% | 87 min | 6.77% | A− |
| Republic Airwaysthin sample | 100 | 84.7% | 108 min | 2.00% | B |
| American Airlines | 630 | 81.3% | 118 min | 1.11% | B |
| Southwest Airlines | 724 | 76.3% | 57 min | 0.55% | B+ |
No carrier stands out. American tops the table at 81.3%, 5 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Best ways to make this trip
The most reliable ways to fly St. Louis 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. STL → PHLSt. Louis to Philadelphia | American Airlines | 80.4% | 81.3% | 1.11% | 5am–8am, Thu | — |
| 2. STL → PHLSt. Louis to Philadelphia | Southwest Airlines | 75.9% | 76.3% | 0.55% | 8am–11am, Wed | — |
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 27 points, against 5 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am384 flights89.3%
- 8am–11am321 flights89.9%
- 11am–2pm313 flights81.0%
- 2pm–5pm162 flights70.7%
- 5pm–8pm305 flights63.4%
- 8pm–5am102 flights68.7%
Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 63.4% on time, against 89.9% 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 5am–8am window is the busiest, with 384 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 27 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 66.7% on time, 27 points below February, the best at 93.5%. 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. November was the busiest month here, with 162 flights.
Across the week, Wednesday is the strongest day at 84.5% on time and Sunday the weakest at 72.4%. 12 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 51% of the 27,000 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
- 35%Carrier
- 9%National Airspace System
- 4%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 27,000 reported delay minutes here, that single category outweighs weather by 11 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 26,503 reported delay minutes.
The largest share of delay minutes, 35%, 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 9,387 of the 27,000 delay minutes reported here.
Cancellations sit at 1.39% against a national 1.81%, which is ordinary. Diversions add another 0.25%.
Connections and stage length
What a delay here actually costs
7.8% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last an hour and a half, which a normal layover absorbs.
The 814 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg runs 77.1% on time across 1,591 flights, within 3 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 1,587 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. February runs 93.5% on time and July 66.7%, a swing of 27 points. If the dates move at all, move them out of July before you think about anything else. 1,561 completed flights over 12 months sit behind that.
Common questions
STL to PHL questions
How often is STL to PHL delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 20.4% of the 1,587 flights in this analysis, against 22.4% nationally. Delayed flights are late by an hour and a half on average.
Which airline is most reliable on STL to PHL?
American Airlines leads at 81.3% on time across 630 flights. Southwest Airlines is at the other end on 76.3%, a gap of 5 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 STL to PHL?
The 8am–11am departure window is the strongest at 89.9% on time. The 5pm–8pm window is the weakest at 63.4%, 27 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 STL to PHL?
July is the weakest month at 66.7% on time, compared with 93.5% in February. Across the year that is 27 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 STL — the return legseparate record
- St. Louis Lambert International (STL) delay statistics
- Philadelphia International (PHL) delay statistics
- PSA Airlines on STL to PHL85.5%
- Republic Airways on STL to PHL84.7%
- American Airlines on STL to PHL81.3%
- Southwest Airlines on STL to PHL76.3%
- STL to ATL, a related route85.3%
- ATL to PHL, a related route74.9%
- STL to DEN, a related route74.9%
- PSA Airlines on-time record85.5%
- Republic Airways on-time record84.7%
- American Airlines on-time record81.3%
- 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. STL to PHL and PHL to STL 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.