Best time to fly out of St. Louis Lambert (STL)

The early-flight folk wisdom holds up at St. Louis Lambert: departures in the Before 6am band left on time 94% of the time, against 54.6% in the 10pm–12am band. These are historical odds, not forecasts. The records say what happened on this schedule over three years; they know nothing about tomorrow’s thunderstorm.

Data through June 2026 · Bureau of Transportation Statistics

On-time rate by hour and day

On this page, “on time” means a departure that pushed back less than 15 minutes behind its scheduled time — the Bureau of Transportation Statistics definition, and the one airlines are held to.

Share of departures that left on time, by hour band and day of week.
Departure time MonTueWedThuFriSatSun
Before 6am 93 95 95 97 94 92 92
6–8am 89 92 93 92 92 90 90
8–10am 83 88 89 89 87 86 87
10am–12pm 81 87 88 84 83 84 84
12–2pm 74 83 84 79 78 76 75
2–4pm 72 78 77 71 71 72 68
4–6pm 69 74 70 64 65 70 62
6–8pm 68 73 71 62 66 65 59
8–10pm 65 71 68 56 65 50 56
10pm–12am 56 56 53 59 56 54 50
fewer left on time more left on time

The steadiest stretch at STL was Before 6am — 94% of departures left on time across 8,968 flights. The weakest was 10pm–12am at 54.6%. 6–8am departures from STL left on time 91.2% of the time across 27,541 flights; 6–8pm departures, 66.4% across 23,125. That is a gap of 24.8 points, and it is the whole case for the early flight.

The year at STL

July was the hard month at STL: 67.5% of departures left on time, across 17,379 flights. September was the easy one at 83.5%. Each month pools three years of that month, so a single bad week does not decide it.

Share of departures that left on time, by calendar month. Best month in green, worst in amber. The hairline sits at the overall rate, 77.6%.
Departure on-time share at STL by calendar month
Month Share departures that left on time Flights
January 79.3% 14,335
February 83.2% 13,506
March 76.5% 16,230
April 79.9% 16,039
May 73.8% 16,659
June 71.1% 17,021
July 67.5% 17,379
August 78.2% 16,794
September 83.5% 16,163
October 81.8% 17,076
November 82.9% 15,710
December 75.9% 16,013

Airlines at STL

Every airline with at least 100 departures from STL, busiest first. These are that airline’s departures from this airport only — its record across the country sits on its own page.

Airline Left on time Typical delay Cancelled Departures
Southwest Airlines 75% 50 min 0.8% 121,821
American Airlines 81% 118 min 1.7% 19,016
Delta Air Lines 88.3% 91 min 1% 16,373
United Airlines 78.4% 85 min 1.2% 8,170
Republic Airways 86.3% 85 min 3.4% 7,740
Envoy Air 79% 73 min 2% 5,089
SkyWest Airlines 75.4% 104 min 2% 3,785
Frontier Airlines 73.9% 99 min 2.3% 3,585
Alaska Airlines 83.1% 54 min 1% 2,397
Endeavor Air 87% 77 min 3.6% 2,158
PSA Airlines 80% 123 min 4.8% 1,924
Spirit Airlines 66.5% 84 min 3.1% 867

What delays out of STL were put down to

Airlines file a reason with every arrival running 15 minutes late or more. Across 39,388 flights that departed STL and ran 15 minutes late or more, the delay minutes break down with 45.7% put down to late-arriving aircraft and 31% to airline operations.

Late-arriving aircraft 45.7% Airline operations 31% Air traffic & airport volume 19.2% Severe weather 4% Security 0.2%
  • Late-arriving aircraft 45.7%
  • Airline operations 31%
  • Air traffic & airport volume 19.2%
  • Severe weather 4%
  • Security 0.2%

Late-arriving aircraft is the knock-on category: the plane came in late, so it went out late again. It is why a 7am problem in Newark is still a problem in Denver at dinnertime, and why it is usually the biggest slice on the bar.

If you are connecting through STL

Of 192,931 scheduled arrivals into STL, 79.1% reached the gate less than 15 minutes behind schedule. Of the 37,804 arrivals that ran late, 57.4% were no more than 45 minutes behind — which is the difference between a tight connection and a new boarding pass.

Work out a specific layover — pick the airport and the minutes you have, and the tool reads the same arrival records back as a share.

Busiest routes out of STL

Ranked by flights, with the share that arrived on time at the far end. Where a route carries enough flights for a page of its own the chip goes there; otherwise it goes to the destination airport.

STL in one number

St. Louis Lambert (STL)

Rank 31 of 363 US airports by departures. Steadiest stretch of the day: Before 6am. Hardest month: July.

July 2023–June 2026 · 190,610 departures flown

77.6% of departures left on time

Questions about STL

What is the best time of day to fly out of St. Louis Lambert?
Before 6am. Departures in that band left on time 94% of the time across 8,968 flights, July 2023 through June 2026 — the best of the ten bands in the day. The 10pm–12am band was the weakest at 54.6%.
Is the early flight out of STL really more reliable?
6–8am departures from STL left on time 91.2% of the time across 27,541 flights; 6–8pm departures, 66.4% across 23,125. That is a gap of 24.8 points, and it is the whole case for the early flight.
What is the worst month to fly out of STL?
July: 67.5% of the departures that flew left on time, with 17,379 scheduled. September was the other end of the year at 83.5%. Each figure pools three years of that calendar month.
Which airline is most on time at STL?
Delta Air Lines — 88.3% of its 16,373 departures from STL left on time. Spirit Airlines sat at the other end at 66.5% over 867 flights. Only airlines with at least 100 departures here are ranked.
How often are flights cancelled at STL?
1.2% of scheduled departures were cancelled over July 2023 through June 2026. Cancellations are counted against everything scheduled, not against everything that flew — a rate that looks small still adds up to real people in a rebooking line.