Carrier route record
WNDTW→STL
Southwest Airlines · Detroit to St. Louis
- Flights
- 611
- Period
- September 2025 to August 2026
- Share of route
- 32%
- Carriers
- 4
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on DTW to STL sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.3%. The late ones land about 55 minutes behind schedule. That rests on 611 flights, with a median arrival 7 minutes early.
The US average over the same twelve months is 77.3%, so there is little to separate Southwest on DTW to STL from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
74.3%
Arrivals under 15 minutes late, of 607 completed flights
Avg delay
55 min
Across delayed arrivals only, not all flights
Cancelled
0.65%
National rate is 1.89%
Whole route
76.6%
Every carrier on DTW to STL, 1,899 flights
These figures cover 611 flights between September 2025 and August 2026. The median arrival is 7 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.
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Carrier by carrier
Southwest against every carrier on DTW to STL
Southwest flew 611 of the 1,899 flights on DTW to STL, about 32% of it. Its 74.3% on time is 2 points worse than the route as a whole, which runs 76.6%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from Spirit at 100.0% to SkyWest at 61.2%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Spirit Airlinesthin sample | 1 | 100.0% | — | 0.00% | A+ |
| Delta Air Lines | 1,104 | 80.4% | 63 min | 1.27% | B |
| Southwest Airlines (this page) | 611 | 74.3% | 55 min | 0.65% | C+ |
| SkyWest Airlinesthin sample | 183 | 61.2% | 87 min | 1.64% | D |
Timetable by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Departure window
When Southwest runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 52 points, against half a point between the best and worst carrier.
- 5am–8am241 flights92.0%
- 8am–11am69 flights95.7%
- 11am–2pm26 flights—
- 2pm–5pm46 flights54.3%
- 5pm–8pm86 flights69.8%
- 8pm–5am143 flights44.1%
Scale runs 35% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 44.1% on time, against 95.7% for the 8am–11am 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 5am–8am window is the busiest, with 241 flights scheduled in it.
Across the year
Southwest on DTW to STL through the year
December is the weak month at 56.5% on time, against 93.6% in September. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. August was the busiest month here, with 62 flights.
Across the week, Saturday is the strongest day at 85.5% on time and Friday the weakest at 66.7%, a spread of 19 points.
Arrival by arrival
How late Southwest on DTW to STL runs when it is late
Southwest on DTW to STL often beats the schedule: 165 of 607 completed flights, 27%, arrived 15 minutes or more early. The 156 late arrivals split 58 under half an hour, 53 between 30 and 60 minutes, and 45 an hour or more.
- 15+ min early165 flights27.2%
- Within 15 min286 flights47.1%
- 15–29 min late58 flights9.6%
- 30–59 min late53 flights8.7%
- 1–2 hours late30 flights4.9%
- 2+ hours late15 flights2.5%
Scale runs 0% to 100%.
Share of 607 completed flights by arrival against schedule.
30 of 171 late departures made up the time and arrived on time, 18% of them. 15 flights left on time and still arrived late.
The worst days
Worst days for Southwest on DTW to STL
The latest arrival of the period was on 26 September 2025, 4 hours 11 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 26 September 2025 | 4 hours 11 minutes | Late-arriving aircraft |
| 11 June 2026 | 4 hours 1 minute | Late-arriving aircraft |
| 22 August 2026 | 3 hours 57 minutes | Late-arriving aircraft |
| 14 March 2026 | 3 hours 33 minutes | Carrier |
| 19 May 2026 | 3 hours 14 minutes | Carrier |
Delay causes
Why Southwest runs late on this route
Late-arriving aircraft accounts for 64% of the 8,495 delay minutes carriers reported here, and the remaining four split what is left.
- 64%Late-arriving aircraft
- 23%Carrier
- 11%National Airspace System
- 3%Extreme weather
64% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 8,495 reported delay minutes here, that single category outweighs weather by 22 to one. The split is drawn from 8,495 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 95.7% on time here.
Cancellations are rare at 0.65%, below the national 1.89% 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.
Connections and stage length
What a delay here costs
7.4% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about 55 minutes, which a normal layover absorbs.
At 440 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 8am–11am window matters as much as it does.
The return leg runs 71.5% on time across 611 flights, within 3 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
One caution: this is a thin sample. 611 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Southwest on DTW to STL
Put together: treat all of this as provisional. 611 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 74.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 607 completed flights over 12 months sit behind that.
Related
Where to go next
- DTW to STL, every carrier
- Southwest on STL to DTW, the return leg
- Delta Air Lines on DTW to STL80.4%
- SkyWest Airlines on DTW to STL61.2%
- Southwest Airlines network-wide record
- Detroit Metropolitan Wayne County (DTW) delay statistics
- St. Louis Lambert International (STL) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.