Airport month record
STLMAY
St. Louis Lambert International in May 2026
- Departures
- 5,375
- Month
- May 2026
- National, same month
- 78.6%
- Carriers
- 10
Historical statistics for May 2026, not live status or a forecast for this year’s May. For today’s conditions at STL, see live FAA status.
STL in May lands a B+, about a point worse than the national rate of 78.6%. 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 5,375 flights, of which Delta Air Lines flew 496 at 90.8% on time.
Delta Air Lines is the most reliable of the three carriers covered here at 90.8% on time across 496 flights.
Key figures
On time
77.5%
Arrivals under 15 minutes late, of 5,315 completed departures
Avg delay
74 min
Across delayed arrivals only, not all flights
Cancelled
0.84%
Nationally in May: 0.92%
Whole year
78.0%
STL across all twelve months
These figures cover 5,375 departures from St. Louis Lambert International in May 2026. 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
May next to STL's other months
Against STL's own year, May ran level with the twelve-month rate of 78.0%, which makes it number eight of twelve months, best first. Either side of it, April ran 80.8% on time and June 69.0%, so a trip moved by a few weeks would have landed in a worse 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 | 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 (this page) | 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 May
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 30 points, against 16 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am982 flights92.1%
- 8am–11am1,194 flights86.1%
- 11am–2pm709 flights78.5%
- 2pm–5pm876 flights73.2%
- 5pm–8pm994 flights65.3%
- 8pm–5am620 flights62.2%
Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 62.2% on time, against 92.1% 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 1,194 flights scheduled in it.
Across the week, Saturday is the strongest day at 81.8% on time and Monday the weakest at 65.5%. 16 points is a smaller lever than departure hour, but it is free.
Carrier by carrier
Which airlines ran best at STL in May
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 90.8% of the time; Southwest Airlines manages 74.7%. Sample sizes sit next to every figure, because a two-point gap across 3,236 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlines | 3,236 | 74.7% | 59 min | 0.43% | C+ |
| American Airlines | 543 | 81.3% | 136 min | 1.10% | B |
| Delta Air Lines | 496 | 90.8% | 85 min | 1.21% | A |
| Republic Airwaysthin sample | 246 | 85.0% | 95 min | 2.03% | A |
| SkyWest Airlinesthin sample | 221 | 69.4% | 100 min | 2.26% | C |
| United Airlinesthin sample | 191 | 78.9% | 77 min | 0.52% | B+ |
| Envoy Airthin sample | 123 | 83.5% | 101 min | 1.63% | B |
| Frontier Airlinesthin sample | 123 | 76.0% | 105 min | 1.63% | B |
| Alaska Airlinesthin sample | 100 | 82.0% | 50 min | 0.00% | B+ |
| PSA Airlinesthin sample | 96 | 70.7% | 138 min | 4.17% | C− |
The spread between Delta and Southwest is 16 points, wide enough that it should decide the booking. On a hundred trips that is 16 more arrivals inside the on-time window.
Route by route
Busiest routes out of STL in May
| Route | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| STL to ATL · Atlantathin sample | 330 | 81.5% | 60 min | 1.21% | B |
| STL to ORD · Chicagothin sample | 322 | 80.4% | 112 min | 1.86% | B |
| STL to DEN · Denverthin sample | 310 | 71.8% | 74 min | 0.32% | C+ |
| STL to LGA · New Yorkthin sample | 234 | 74.4% | 70 min | 2.99% | C |
| STL to MCO · Orlandothin sample | 218 | 79.2% | 54 min | 0.46% | B+ |
| STL to DFW · Dallas-Fort Worththin sample | 208 | 74.7% | 179 min | 4.33% | C− |
| STL to PHX · Phoenixthin sample | 202 | 73.6% | 54 min | 0.50% | C+ |
| STL to DCA · Washingtonthin sample | 197 | 73.2% | 88 min | 1.52% | C |
| STL to DTW · Detroitthin sample | 179 | 82.4% | 70 min | 1.68% | B |
| STL to MSP · Minneapolisthin sample | 172 | 87.8% | 80 min | 0.00% | A+ |
| STL to LAS · Las Vegasthin sample | 171 | 79.9% | 78 min | 0.00% | B+ |
| STL to DAL · Dallasthin sample | 167 | 73.0% | 70 min | 1.80% | C |
| STL to MDW · Chicagothin sample | 157 | 83.9% | 36 min | 1.27% | B |
| STL to PHL · Philadelphiathin sample | 143 | 70.4% | 63 min | 0.00% | C+ |
| STL to BOS · Bostonthin sample | 142 | 64.1% | 83 min | 0.00% | D+ |
| STL to CLT · Charlottethin sample | 139 | 86.3% | 127 min | 0.00% | A+ |
| STL to HOU · Houstonthin sample | 131 | 72.9% | 56 min | 0.00% | C+ |
| STL to TPA · Tampathin sample | 115 | 80.7% | 64 min | 0.87% | B+ |
| STL to BNA · Nashvillethin sample | 114 | 78.8% | 43 min | 0.88% | B+ |
| STL to BWI · Baltimorethin sample | 112 | 86.6% | 63 min | 0.00% | A+ |
| STL to EWR · Newarkthin sample | 93 | 93.3% | 138 min | 2.15% | A |
| STL to AUS · Austinthin sample | 92 | 67.0% | 74 min | 0.00% | C+ |
| STL to MIA · Miamithin sample | 90 | 86.7% | 80 min | 0.00% | A+ |
| STL to MCI · Kansas Citythin sample | 88 | 73.9% | 62 min | 0.00% | C+ |
| STL to SLC · Salt Lake Citythin sample | 87 | 95.3% | 120 min | 1.15% | A |
Delay causes
What held STL up in May
One category carries most of the weight here. Late-arriving aircraft accounts for 47% of the 88,000 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.
- 47%Late-arriving aircraft
- 27%Carrier
- 21%National Airspace System
- 4%Extreme weather
- 0%Security
47% 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 88,000 reported delay minutes here, that single category outweighs weather by 11 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 88,104 reported delay minutes.
Cancellations are rare at 0.84%, below the national 0.92% 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.
8.0% of arrivals land an hour or more late, close to the national 7.1%. 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.
What to do with this
Flying from STL in May
For a May trip through STL: expect 77.5% on time and 0.84% cancelled, going by May 2026. The 5am–8am window was the strongest part of the day.
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 December74.0%
- STL in January83.1%
- STL in February84.9%
- STL in March75.3%
- STL in April80.8%
- 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.