Carrier route record

WNSFO→STL

Southwest Airlines · San Francisco to St. Louis

Flights: 342
Period: July 2025 to June 2026
Share of route: 44%
Carriers: 3

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.

Southwest on SFO to STL earns an F+, which is as low as this site's scale goes for a reason. Only 49.0% of flights arrive inside the 15-minute window, 29 points worse than the national rate of 77.6%. Late arrivals average about an hour. Treat any tight connection here as a coin flip. That rests on 342 flights, with a median arrival 15 minutes late.

The national on-time rate over the same period is 77.6%, so Southwest on SFO to STL runs 29 points behind the country as a whole. Across a thousand flights that is about 286 extra late arrivals.

On time

49.0%

Arrivals under 15 minutes late, of 341 completed flights

Avg delay

59 min

Across delayed arrivals only, not all flights

Cancelled

0.00%

National rate is 1.81%

Whole route

65.8%

Every carrier on SFO to STL, 781 flights

These figures cover 342 flights between July 2025 and June 2026. Beyond the headline rate, 21.1% 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 SFO to STL

Southwest flew 342 of the 781 flights on SFO to STL, about 44% of it. Its 49.0% on time is 17 points worse than the route as a whole, which runs 65.8%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from United at 80.7% to Southwest at 49.0%. 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.

On-time performance by carrier on SFO to STL
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlinesthin sample	204	80.7%	52 min	0.49%	B+
SkyWest Airlinesthin sample	235	77.6%	85 min	2.55%	B
Southwest Airlines (this page)thin sample	342	49.0%	59 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 11 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–11am112 flights54.5%
11am–2pm217 flights43.5%
2pm–5pm—
5pm–8pm—
8pm–5am—

Scale runs 35% to 60%. Rows with fewer than 30 flights show a dash.

The weak window here is the middle of the day, not the evening: 11am–2pm runs 43.5% on time against 54.5% for 8am–11am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 11am–2pm window is the busiest, with 217 flights scheduled in it.

Across the year

Southwest on SFO to STL through the year

Jul–Sep 202592 flights62.0%
Oct–Dec 202587 flights44.2%
Jan–Mar 202681 flights71.6%
Apr–Jun 202682 flights17.1%

Scale runs 10% to 75%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 49.0% on time across 342 flights.

Southwest on SFO to STL did not run the same all year. Its best quarter was Jan–Mar 2026 at 71.6% on time and its weakest Apr–Jun 2026 at 17.1%, a swing of 54 points on roughly 86 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.

Across the week, Saturday is the strongest day at 63.3% on time and Monday the weakest at 32.7%. 31 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 70% of the 10,000 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.

Late-arriving aircraft
70%
Carrier
22%
National Airspace System
8%

70% 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 10,000 reported delay minutes here, that single category outweighs weather by 70 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 10,244 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 54.5% on time here.

Cancellations are rare at 0.00%, below the national 1.81% and low enough to earn the plus on the grade. Almost no flights are 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. 21.1% 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 1,735 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 62.5% on time across 342 flights, 14 points above this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 14 points of difference.

One caution: this is a thin sample. 342 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 SFO to STL

Put together: treat all of this as provisional. 342 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 49.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 341 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures