Carrier route record
WNSTL→DTW
Southwest Airlines · St. Louis to Detroit
- 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 STL to DTW sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, 4 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 593 flights, with a median arrival 1 minute early.
The national on-time rate over the same period is 77.6%, so Southwest on STL to DTW runs 4 points behind the country as a whole. Across a thousand flights that is about 40 extra late arrivals.
Key figures
On time
73.6%
Arrivals under 15 minutes late, of 591 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
0.34%
National rate is 1.81%
Whole route
81.8%
Every carrier on STL to DTW, 1,905 flights
These figures cover 593 flights between July 2025 and June 2026. Beyond the headline rate, 9.1% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Carrier by carrier
Southwest against every carrier on STL to DTW
Southwest flew 593 of the 1,905 flights on STL to DTW, about 31% of it. Its 73.6% on time is 8 points worse than the route as a whole, which runs 81.8%. Ranked by on-time rate it is number three of five carriers on the route, where the range runs from Delta at 88.2% 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 |
|---|---|---|---|---|---|
| Delta Air Lines | 1,088 | 88.2% | 102 min | 1.65% | A |
| Spirit Airlinesthin sample | 36 | 83.3% | 206 min | 0.00% | B+ |
| Southwest Airlines (this page) | 593 | 73.6% | 62 min | 0.34% | C+ |
| SkyWest Airlinesthin sample | 186 | 71.7% | 110 min | 1.08% | C |
| Republic Airwaysthin sample | 2 | 0.0% | 37 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 38 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–8am13 flights—
- 8am–11am147 flights90.5%
- 11am–2pm65 flights80.0%
- 2pm–5pm17 flights—
- 5pm–8pm245 flights69.7%
- 8pm–5am106 flights52.4%
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 52.4% on time, against 90.5% 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 5pm–8pm window is the busiest, with 245 flights scheduled in it.
Across the year
Southwest on STL to DTW through the year
June is the worst month at 53.3% on time, 34 points below September, the best at 87.2%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. May was the busiest month here, with 61 flights.
Across the week, Tuesday is the strongest day at 81.7% on time and Thursday the weakest at 65.2%. 17 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 63% of the 9,725 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.
- 63%Late-arriving aircraft
- 29%Carrier
- 6%National Airspace System
- 1%Extreme weather
63% 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 9,725 reported delay minutes here, that single category outweighs weather by 63 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 9,725 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 90.5% on time here.
Cancellations are rare at 0.34%, 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
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.1% of arrivals land a full hour or more behind schedule, against 8.1% 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.
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 75.9% 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 STL to DTW
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 73.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 591 completed flights over 12 months sit behind that.
Related
Where to go next
- STL to DTW, every carrier
- Southwest on DTW to STL, the return leg
- Delta Air Lines on STL to DTW88.2%
- SkyWest Airlines on STL to DTW71.7%
- Southwest Airlines network-wide record
- St. Louis Lambert International (STL) delay statistics
- Detroit Metropolitan Wayne County (DTW) 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.