Airport month record
STLDEC
St. Louis Lambert International in December 2025
- Departures
- 5,359
- Month
- December 2025
- National, same month
- 73.2%
- Carriers
- 10
Historical statistics for December 2025, not live status or a forecast for this year’s December. For today’s conditions at STL, see live FAA status.
STL in December sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, about a point better than the national rate of 73.2%. The late ones land a little over an hour behind schedule. That rests on 5,359 flights, of which Delta Air Lines flew 430 at 80.1% on time.
Delta Air Lines is the most reliable of the three carriers covered here at 80.1% on time across 430 flights.
Key figures
On time
74.0%
Arrivals under 15 minutes late, of 5,304 completed departures
Avg delay
75 min
Across delayed arrivals only, not all flights
Cancelled
0.90%
Nationally in December: 1.55%
Whole year
78.0%
STL across all twelve months
These figures cover 5,359 departures from St. Louis Lambert International in December 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
December next to STL's other months
Against STL's own year, December ran 4 points worse than the twelve-month rate of 78.0%, which makes it number ten of twelve months, best first. Either side of it, November ran 80.1% on time and January 83.1%, so a trip moved by a few weeks would have landed in a better stretch.
| 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 | 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 (this page) | 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 December
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 26 points, against 6 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am958 flights87.3%
- 8am–11am1,230 flights82.1%
- 11am–2pm629 flights69.5%
- 2pm–5pm910 flights68.7%
- 5pm–8pm914 flights67.7%
- 8pm–5am718 flights61.2%
Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 61.2% on time, against 87.3% 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 1,230 flights scheduled in it.
Across the week, Wednesday is the strongest day at 80.8% on time and Saturday the weakest at 66.7%. 14 points is a smaller lever than departure hour, but it is free.
Carrier by carrier
Which airlines ran best at STL in December
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 80.1% of the time; Southwest Airlines manages 74.1%. Sample sizes sit next to every figure, because a two-point gap across 3,453 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlines | 3,453 | 74.1% | 59 min | 0.32% | C+ |
| Delta Air Lines | 430 | 80.1% | 97 min | 2.56% | B |
| American Airlines | 396 | 79.5% | 113 min | 0.25% | B+ |
| Republic Airwaysthin sample | 341 | 71.7% | 118 min | 2.64% | C |
| United Airlinesthin sample | 180 | 71.7% | 100 min | 0.00% | C+ |
| SkyWest Airlinesthin sample | 159 | 56.9% | 111 min | 3.77% | D− |
| Envoy Airthin sample | 126 | 76.4% | 67 min | 2.38% | B |
| Frontier Airlinesthin sample | 114 | 68.8% | 104 min | 1.75% | C |
| PSA Airlinesthin sample | 96 | 81.5% | 141 min | 4.17% | B− |
| Alaska Airlinesthin sample | 54 | 54.7% | 55 min | 1.85% | F |
Delta leads Southwest by 6 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 December
| Route | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| STL to ATL · Atlantathin sample | 311 | 80.7% | 77 min | 1.61% | B |
| STL to DEN · Denverthin sample | 266 | 69.1% | 80 min | 0.00% | C+ |
| STL to ORD · Chicagothin sample | 240 | 62.7% | 99 min | 2.92% | D |
| STL to LGA · New Yorkthin sample | 230 | 67.6% | 82 min | 2.17% | C |
| STL to MCO · Orlandothin sample | 222 | 70.0% | 76 min | 0.45% | C+ |
| STL to PHX · Phoenixthin sample | 206 | 70.9% | 64 min | 0.00% | C+ |
| STL to DCA · Washingtonthin sample | 203 | 74.9% | 56 min | 1.97% | C |
| STL to DFW · Dallas-Fort Worththin sample | 199 | 76.1% | 128 min | 1.01% | B |
| STL to LAS · Las Vegasthin sample | 186 | 75.8% | 74 min | 0.00% | B+ |
| STL to CLT · Charlottethin sample | 166 | 78.3% | 121 min | 0.00% | B+ |
| STL to DTW · Detroitthin sample | 156 | 78.1% | 123 min | 3.21% | B− |
| STL to DAL · Dallasthin sample | 153 | 77.5% | 62 min | 1.31% | B |
| STL to PHL · Philadelphiathin sample | 148 | 78.2% | 79 min | 0.68% | B+ |
| STL to BOS · Bostonthin sample | 146 | 80.0% | 72 min | 0.68% | B+ |
| STL to MSP · Minneapolisthin sample | 144 | 68.6% | 76 min | 2.78% | C |
| STL to MDW · Chicagothin sample | 139 | 78.3% | 64 min | 0.72% | B+ |
| STL to HOU · Houstonthin sample | 138 | 70.3% | 44 min | 0.00% | C+ |
| STL to TPA · Tampathin sample | 108 | 81.1% | 60 min | 0.00% | B+ |
| STL to LAX · Los Angelesthin sample | 103 | 70.9% | 41 min | 0.00% | C+ |
| STL to BNA · Nashvillethin sample | 102 | 78.4% | 67 min | 0.00% | B+ |
| STL to BWI · Baltimorethin sample | 101 | 81.0% | 56 min | 0.99% | B+ |
| STL to MIA · Miamithin sample | 99 | 78.8% | 48 min | 0.00% | B+ |
| STL to AUS · Austinthin sample | 91 | 70.3% | 44 min | 0.00% | C+ |
| STL to RSW · Fort Myersthin sample | 87 | 72.9% | 60 min | 1.15% | C |
| STL to MCI · Kansas Citythin sample | 85 | 59.5% | 44 min | 1.18% | D |
Delay causes
What held STL up in December
One category carries most of the weight here. Late-arriving aircraft accounts for 46% of the 103,000 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
- 18%National Airspace System
- 5%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 103,000 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 102,796 reported delay minutes.
Cancellations sit at 0.90% against a national 1.55%, which is ordinary. Diversions add another 0.13%.
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.6% of arrivals land a full hour or more behind schedule, against 10.0% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
What to do with this
Flying from STL in December
For a December trip through STL: plan on this being one of the airport's harder months. The 5am–8am departures held up best at 87.3% on time, and with 9.6% of arrivals an hour or more late, a connection here deserves more slack than the same trip in February would.
Related
Where to go next
- St. Louis Lambert International (STL), the whole year
- STL in July71.7%
- STL in August79.7%
- STL in September83.8%
- STL in October78.5%
- STL in November80.1%
- 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.