Airport month record

STLSEP

St. Louis Lambert International in September 2025

Departures: 5,321
Month: September 2025
National, same month: 83.4%
Carriers: 9

Historical statistics for September 2025, not live status or a forecast for this year’s September. For today’s conditions at STL, see live FAA status.

STL in September lands a B+, level with the national rate of 83.4%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 5,321 flights, of which Delta Air Lines flew 477 at 94.5% on time.

Delta Air Lines is the most reliable of the three carriers covered here at 94.5% on time across 477 flights.

On time

83.8%

Arrivals under 15 minutes late, of 5,287 completed departures

Avg delay

58 min

Across delayed arrivals only, not all flights

Cancelled

0.34%

Nationally in September: 0.51%

Whole year

78.0%

STL across all twelve months

These figures cover 5,321 departures from St. Louis Lambert International in September 2025. On time means an arrival less than 15 minutes after the scheduled gate time, the DOT's threshold, and the national comparison uses every US departure in the same month rather than the whole year.

Against the year

September next to STL's other months

Against STL's own year, September ran 6 points better than the twelve-month rate of 78.0%, which makes it number two of twelve months, best first. Cancellations were unusually low for STL in September, at 0.34% against 1.28% across the year. Either side of it, August ran 79.7% on time and October 78.5%, so a trip moved by a few weeks would have landed in a worse stretch.

STL month by month
Month	Flights	On time	Avg delay	Cancelled	Grade
July 2025	5,855	71.7%	73 min	1.57%	C
August 2025	5,539	79.7%	71 min	0.96%	B+
September 2025 (this page)	5,321	83.8%	58 min	0.34%	B+
October 2025	5,611	78.5%	60 min	0.27%	B+
November 2025	5,202	80.1%	76 min	1.46%	B
December 2025	5,359	74.0%	75 min	0.90%	C+
January 2026	4,683	83.1%	74 min	3.46%	B−
February 2026	4,484	84.9%	64 min	1.32%	B
March 2026	5,400	75.3%	74 min	2.52%	B
April 2026	5,156	80.8%	65 min	0.80%	B+
May 2026	5,375	77.5%	74 min	0.84%	B+
June 2026	5,463	69.0%	68 min	1.17%	C

Departure window

The best time of day to leave STL in September

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 19 points, against 12 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am948 flights93.2%
8am–11am1,359 flights91.7%
11am–2pm634 flights84.3%
2pm–5pm905 flights76.0%
5pm–8pm955 flights75.9%
8pm–5am520 flights73.9%

Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 93.2% of the time, against 73.9% for the overnight window. That is 19 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 1,359 flights scheduled in it.

Across the week, Wednesday is the strongest day at 88.4% on time and Thursday the weakest at 79.4%. 9 points is a smaller lever than departure hour, but it is free.

Carrier by carrier

Which airlines ran best at STL in September

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 94.5% of the time; Southwest Airlines manages 82.9%. Sample sizes sit next to every figure, because a two-point gap across 3,361 flights means less than a ten-point one.

Carriers at STL in September 2025
Airline	Flights	On time	Avg delay	Cancelled	Grade
Southwest Airlines	3,361	82.9%	48 min	0.09%	B+
American Airlines	503	83.8%	123 min	1.39%	B
Delta Air Lines	477	94.5%	76 min	0.21%	A+
United Airlinesthin sample	235	79.9%	59 min	0.00%	B+
Republic Airwaysthin sample	232	84.6%	66 min	1.72%	B
SkyWest Airlinesthin sample	194	79.1%	59 min	1.03%	B
Envoy Airthin sample	134	85.1%	59 min	0.00%	A+
Frontier Airlinesthin sample	93	78.0%	51 min	1.08%	B
Alaska Airlinesthin sample	77	85.7%	25 min	0.00%	A+

Delta leads Southwest by 12 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Route by route

Busiest routes out of STL in September

Routes from STL in September 2025
Route	Flights	On time	Avg delay	Cancelled	Grade
STL to DEN · Denverthin sample	326	77.8%	46 min	0.00%	B+
STL to ATL · Atlantathin sample	317	95.0%	47 min	0.00%	A+
STL to ORD · Chicagothin sample	239	81.0%	70 min	0.84%	B+
STL to DCA · Washingtonthin sample	217	76.4%	62 min	0.46%	B+
STL to LGA · New Yorkthin sample	204	86.0%	50 min	0.49%	A+
STL to DFW · Dallas-Fort Worththin sample	193	75.1%	70 min	2.07%	B
STL to DAL · Dallasthin sample	172	78.4%	46 min	0.00%	B+
STL to MSP · Minneapolisthin sample	170	81.2%	78 min	0.00%	B+
STL to LAS · Las Vegasthin sample	165	79.6%	47 min	0.61%	B+
STL to PHX · Phoenixthin sample	160	77.6%	51 min	1.25%	B
STL to CLT · Charlottethin sample	155	89.0%	163 min	0.65%	A+
STL to MCO · Orlandothin sample	155	85.2%	58 min	0.00%	A+
STL to MDW · Chicagothin sample	151	83.4%	38 min	0.00%	B+
STL to DTW · Detroitthin sample	148	93.9%	52 min	0.00%	A+
STL to BOS · Bostonthin sample	142	70.2%	70 min	0.70%	C+
STL to PHL · Philadelphiathin sample	132	81.8%	119 min	0.00%	B+
STL to HOU · Houstonthin sample	125	85.5%	29 min	0.80%	A+
STL to BWI · Baltimorethin sample	116	79.3%	53 min	0.00%	B+
STL to BNA · Nashvillethin sample	108	93.5%	36 min	0.00%	A+
STL to EWR · Newarkthin sample	106	84.5%	83 min	2.83%	B
STL to SEA · Seattlethin sample	98	82.7%	25 min	0.00%	B+
STL to TPA · Tampathin sample	90	84.4%	34 min	0.00%	B+
STL to MCI · Kansas Citythin sample	90	84.4%	62 min	0.00%	B+
STL to SLC · Salt Lake Citythin sample	82	91.4%	74 min	1.22%	A
STL to LAX · Los Angelesthin sample	82	86.6%	39 min	0.00%	A+

Delay causes

What held STL up in September

One category carries most of the weight here. Late-arriving aircraft accounts for 45% of the 49,000 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.

Late-arriving aircraft
45%
Carrier
33%
National Airspace System
20%
Extreme weather
2%

45% 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 49,000 reported delay minutes here, that single category outweighs weather by 21 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 49,233 reported delay minutes.

Cancellations are rare at 0.34%, below the national 0.51% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.

Badly late arrivals are rare here: only 4.1% land an hour or more behind schedule, against 5.4% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

What to do with this

Flying from STL in September

For a September trip through STL: this is one of the better months to be flying from here, 83.8% on time with 0.34% cancelled. That is a base rate for the month as a whole; a single storm can still spoil a particular day.

St. Louis Lambert International (STL), the whole year
STL in July71.7%
STL in August79.7%
STL in October78.5%
STL in November80.1%
STL in December74.0%
STL in January83.1%
STL in February84.9%
STL in March75.3%
STL in April80.8%
STL in May77.5%
STL in June69.0%

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.

Key figures