St. Louis, MO · departure reliability

STL

St. Louis Lambert International

Departures: 63,448
Period: July 2025 to June 2026
Carriers: 10
US rank: #31 by volume

Terminal building and aircraft stands at a US airport

St. Louis

St. Louis Lambert International lands a B, level with the national rate of 77.6%. Roughly one flight in five arrive 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 63,448 flights, of which Delta Air Lines flew 5,323 at 87.9% on time.

Delta Air Lines is the most reliable of the ten carriers covered here at 87.9% on time across 5,323 flights.

On time

78.0%

Departures arriving under 15 minutes late at their destination

Avg delay

70 min

Across delayed flights only

Cancelled

1.28%

National rate is 1.81%

Best carrier

Delta

87.9% on time here

These figures cover 63,000 flights between July 2025 and June 2026. The median arrival is 6 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 airlines run best out of STL

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 87.9% of the time; SkyWest Airlines manages 69.3%. Sample sizes sit next to every figure, because a two-point gap across 2,359 flights means less than a ten-point one.

On-time performance by carrier departing STL
Airline	Flights	On time	Avg delay	Cancelled	Grade
Southwest Airlines	39,703	77.1%	55 min	0.66%	B+
American Airlines	5,833	80.5%	117 min	2.02%	B
Delta Air Lines	5,323	87.9%	90 min	1.56%	A
Republic Airways	3,188	79.5%	84 min	4.42%	B−
SkyWest Airlines	2,359	69.3%	103 min	2.54%	C
United Airlines	2,290	74.0%	83 min	0.87%	C+
Envoy Air	1,592	77.4%	83 min	2.20%	B
Frontier Airlines	1,337	72.9%	100 min	2.32%	C
PSA Airlines	874	76.0%	131 min	5.61%	B−
Alaska Airlines	830	81.1%	48 min	0.96%	B+

PSA Airlines cancels 5.6% of what it schedules here, the highest in the table. A cancelled flight never appears in an on-time rate, so read that column alongside the punctuality one rather than after it.

Route by route

Busiest routes out of STL

Route-level records vary far more than the airport average. These are the 25 busiest departures from STL, each with its own on-time rate against the airport-wide 78.0%.

Busiest routes from STL by flight volume
Route	Flights	On time	Avg delay	Cancelled	Grade
STL to ATL · Atlanta	3,705	85.3%	72 min	1.73%	A
STL to DEN · Denver	3,655	74.9%	70 min	0.41%	C+
STL to ORD · Chicago	3,070	71.1%	97 min	3.22%	C−
STL to LGA · New York	2,645	74.9%	67 min	3.78%	C−
STL to MCO · Orlando	2,497	78.0%	62 min	0.96%	B+
STL to DCA · Washington	2,414	72.9%	76 min	2.65%	C
STL to DFW · Dallas-Fort Worth	2,380	74.5%	111 min	3.40%	C−
STL to PHX · Phoenix	2,284	75.3%	76 min	0.48%	B+
STL to LAS · Las Vegas	2,066	76.8%	68 min	0.58%	B+
STL to DAL · Dallas	1,925	76.2%	61 min	1.51%	B
STL to DTW · Detroit	1,905	81.8%	87 min	1.15%	B
STL to MSP · Minneapolis	1,896	79.8%	78 min	0.95%	B+
STL to CLT · Charlotte	1,827	83.5%	100 min	1.31%	B
STL to MDW · Chicago	1,704	79.7%	55 min	1.12%	B
STL to BOS · Boston	1,610	70.3%	67 min	1.49%	C
STL to PHL · Philadelphia	1,587	79.6%	83 min	1.39%	B
STL to HOU · Houston	1,533	79.3%	54 min	0.20%	B+
STL to BWI · Baltimore	1,281	80.7%	61 min	1.25%	B
STL to BNA · Nashville	1,275	82.8%	54 min	0.63%	B+
STL to TPA · Tampa	1,225	79.6%	54 min	0.65%	B+
STL to MIA · Miami	1,144	82.8%	61 min	0.70%	B+
STL to EWR · Newark	1,075	81.3%	94 min	4.56%	B−
STL to LAX · Los Angeles	1,028	74.0%	64 min	0.19%	C+
STL to MCI · Kansas City	1,020	75.1%	55 min	0.29%	B+
STL to RSW · Fort Myers	1,004	78.6%	52 min	0.50%	B+

Departure window

The best time of day to leave STL

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 25 points, against 19 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am11,610 flights89.7%
8am–11am14,818 flights87.1%
11am–2pm7,850 flights78.2%
2pm–5pm10,363 flights71.8%
5pm–8pm11,356 flights68.3%
8pm–5am7,451 flights64.7%

Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 64.7% on time, against 89.7% 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 14,818 flights scheduled in it.

Across the year

When STL runs late

STL's year swings by 16 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.

Darker means more delays. Figures are on-time percentages.February best, June worst

June is the worst month at 69.0% on time, 16 points below February, the best at 84.9%. 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. July was the busiest month here, with 5,855 flights.

Across the week, Wednesday is the strongest day at 83.3% on time and Sunday the weakest at 73.0%. 10 points is a smaller lever than departure hour, but it is free.

Delay causes

Why STL gets delayed

One category carries most of the weight here. Late-arriving aircraft accounts for 45% of the 959,000 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
31%
National Airspace System
19%
Extreme weather
5%
Security
0%

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 959,000 reported delay minutes here, that single category outweighs weather by 10 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 959,081 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 89.7% on time here.

Cancellations sit at 1.28% against a national 1.81%, which is ordinary. Diversions add another 0.27%.

7.4% 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 are the a little over an hour kind, which a normal layover absorbs.

63,448 flights sit behind these numbers, which is a large enough sample that the headline rate is not moving on noise. Where a sub-group falls below 30 flights the site shows a dash instead of a percentage.

What to do with this

Flying out of STL

Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 84.9% on time and June 69.0%, a swing of 16 points. If the dates move at all, move them out of June before you think about anything else. 62,469 completed flights over 12 months sit behind that.

Common questions

STL delay questions

How often is St. Louis (STL) delayed?

Roughly one flight in five arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.0% of the 63,448 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 St. Louis (STL)?

Delta Air Lines leads at 87.9% on time across 5,323 flights. SkyWest Airlines is at the other end on 69.3%, a gap of 19 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 St. Louis (STL)?

The 5am–8am departure window is the strongest at 89.7% on time. The 8pm–5am window is the weakest at 64.7%, 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 June delays on St. Louis (STL)?

June is the weakest month at 69.0% on time, compared with 84.9% in February. Across the year that is 16 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures