Carrier route record
WNDTW→STL
Southwest Airlines · Detroit to St. Louis
- Flights
- 593
- Period
- July 2025 to June 2026
- Share of route
- 31%
- Carriers
- 5
Historical statistics for July 2025 to June 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 B+. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.6%. The late ones land roughly 50 minutes behind schedule. That rests on 593 flights, with a median arrival 6 minutes early.
The US average over the same twelve months is 77.6%, 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
75.9%
Arrivals under 15 minutes late, of 590 completed flights
Avg delay
51 min
Across delayed arrivals only, not all flights
Cancelled
0.51%
National rate is 1.81%
Whole route
77.0%
Every carrier on DTW to STL, 1,905 flights
These figures cover 593 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
Southwest against every carrier on DTW to STL
Southwest flew 593 of the 1,905 flights on DTW to STL, about 31% of it. Its 75.9% on time is about level with the route as a whole at 77.0%. Ranked by on-time rate it is number three of five carriers on the route, where the range runs from Spirit at 83.3% to Republic at 0.0%. Three 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 | 36 | 83.3% | 100 min | 0.00% | B+ |
| Delta Air Lines | 1,088 | 80.1% | 66 min | 1.19% | B |
| Southwest Airlines (this page) | 593 | 75.9% | 51 min | 0.51% | B+ |
| SkyWest Airlinesthin sample | 186 | 61.3% | 86 min | 1.61% | D |
| Republic Airwaysthin sample | 2 | 0.0% | 26 min | 0.00% | F+ |
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 48 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am216 flights92.1%
- 8am–11am88 flights96.6%
- 11am–2pm27 flights—
- 2pm–5pm32 flights50.0%
- 5pm–8pm73 flights75.3%
- 8pm–5am157 flights49.0%
Scale runs 40% to 100%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 49.0% on time, against 96.6% 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 216 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. May was the busiest month here, with 61 flights.
Across the week, Saturday is the strongest day at 83.8% on time and Sunday the weakest at 68.2%. 16 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
One category carries most of the weight here. Late-arriving aircraft accounts for 60% of the 7,282 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.
- 60%Late-arriving aircraft
- 25%Carrier
- 13%National Airspace System
- 2%Extreme weather
60% 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 7,282 reported delay minutes here, that single category outweighs weather by 32 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 7,282 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 96.6% on time here.
Cancellations are rare at 0.51%, below the national 1.81% 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
6.3% 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 last roughly 50 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 73.6% on time across 593 flights, within 2 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. 593 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. 593 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 75.9% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 590 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 STL80.1%
- SkyWest Airlines on DTW to STL61.3%
- 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 7.04 million flight records
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.