Route reliability record
PHL→STL
Philadelphia to St. Louis
- Flights
- 1,591
- Period
- July 2025 to June 2026
- Distance
- 814 mi
- Carriers
- 4
This route lands a B, level with the national rate of 77.6%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 1,591 PHL to STL flights, of which Southwest Airlines flew 725 at 78.4% on time.
Best time to fly PHL to STL: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 92.0% of the time and Wednesday flights 82.3%, against 77.1% 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
77.1%
Arrivals under 15 minutes late, of 1,567 completed flights
Avg delay
72 min
Across delayed arrivals only, not all flights
Cancelled
1.38%
National rate is 1.81%
Best carrier
Southwest
78.4% on time across 725 flights
These figures cover 1,591 flights between July 2025 and June 2026. Beyond the headline rate, 8.6% 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 PHL to STL
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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Republic Airwaysthin sample | 100 | 85.9% | 64 min | 1.00% | A |
| Southwest Airlines | 725 | 78.4% | 69 min | 0.28% | B+ |
| PSA Airlinesthin sample | 133 | 76.0% | 69 min | 9.02% | B− |
| American Airlines | 633 | 74.4% | 75 min | 1.11% | C |
No carrier stands out. Southwest tops the table at 78.4%, 4 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 Philadelphia to St. Louis
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. PHL → STLPhiladelphia to St. Louis | Southwest Airlines | 78.2% | 78.4% | 0.28% | 5am–8am, Fri | — |
| 2. PHL → STLPhiladelphia to St. Louis | American Airlines | 73.6% | 74.4% | 1.11% | 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 25 points, against 4 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am188 flights92.0%
- 8am–11am293 flights86.6%
- 11am–2pm243 flights78.3%
- 2pm–5pm261 flights73.4%
- 5pm–8pm405 flights67.5%
- 8pm–5am201 flights71.6%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 92.0% of the time, against 67.5% for the evening window. That is 25 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 405 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 29 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 62.1% on time, 29 points below February, the best at 90.9%. 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 163 flights.
Across the week, Wednesday is the strongest day at 82.3% on time and Thursday the weakest at 70.6%. 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 46% of the 26,000 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.
- 46%Late-arriving aircraft
- 30%Carrier
- 17%National Airspace System
- 7%Extreme weather
- 0%Security
46% 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 26,000 reported delay minutes here, that single category outweighs weather by 7 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 25,705 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 92.0% on time here.
Cancellations sit at 1.38% against a national 1.81%, which is ordinary. Diversions add another 0.13%.
Connections and stage length
What a delay here actually costs
8.6% 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 a little over an hour, 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 79.6% on time across 1,587 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 1,591 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 STL 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 90.9% on time and July 62.1%, a swing of 29 points. If the dates move at all, move them out of July before you think about anything else. 1,567 completed flights over 12 months sit behind that.
Common questions
PHL to STL questions
How often is PHL to STL 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 22.9% of the 1,591 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 PHL to STL?
Southwest Airlines leads at 78.4% on time across 725 flights. American Airlines is at the other end on 74.4%, a gap of 4 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 PHL to STL?
The 5am–8am departure window is the strongest at 92.0% on time. The 5pm–8pm window is the weakest at 67.5%, 25 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 PHL to STL?
July is the weakest month at 62.1% on time, compared with 90.9% in February. Across the year that is 29 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
- STL to PHL — the return legseparate record
- Philadelphia International (PHL) delay statistics
- St. Louis Lambert International (STL) delay statistics
- Republic Airways on PHL to STL85.9%
- Southwest Airlines on PHL to STL78.4%
- PSA Airlines on PHL to STL76.0%
- American Airlines on PHL to STL74.4%
- PHL to ATL, a related route79.2%
- ATL to STL, a related route82.4%
- PHL to MCO, a related route72.4%
- Republic Airways on-time record85.9%
- Southwest Airlines on-time record78.4%
- PSA Airlines on-time record76.0%
- 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. PHL to STL and STL to PHL 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.