Carrier route record

WNSTL→SFO

Southwest Airlines · St. Louis to San Francisco

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 STL to SFO draws a D+. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 342 flights, with a median arrival 4 minutes late.

The national on-time rate over the same period is 77.6%, so Southwest on STL to SFO runs 15 points behind the country as a whole. Across a thousand flights that is about 151 extra late arrivals.

On time

62.5%

Arrivals under 15 minutes late, of 341 completed flights

Avg delay

58 min

Across delayed arrivals only, not all flights

Cancelled

0.29%

National rate is 1.81%

Whole route

63.0%

Every carrier on STL to SFO, 782 flights

These figures cover 342 flights between July 2025 and June 2026. Beyond the headline rate, 15.2% 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 SFO

Southwest flew 342 of the 782 flights on STL to SFO, about 44% of it. Its 62.5% on time is about level with the route as a whole at 63.0%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from United at 63.6% to Southwest at 62.5%. 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 STL to SFO
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlinesthin sample	207	63.6%	68 min	0.48%	D+
SkyWest Airlinesthin sample	233	63.2%	96 min	2.15%	D
Southwest Airlines (this page)thin sample	342	62.5%	58 min	0.29%	D+

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 12 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–8am—
8am–11am226 flights62.8%
11am–2pm80 flights75.0%
2pm–5pm7 flights—
5pm–8pm29 flights—
8pm–5am—

Scale runs 55% to 80%. Rows with fewer than 30 flights show a dash.

The best window here is not the first bank but the 11am–2pm slot at 75.0% on time, ahead of 8am–11am at 62.8%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 8am–11am window is the busiest, with 226 flights scheduled in it.

Across the year

Southwest on STL to SFO through the year

Jul–Sep 202592 flights72.5%
Oct–Dec 202587 flights63.2%
Jan–Mar 202681 flights81.5%
Apr–Jun 202682 flights31.7%

Scale runs 25% to 85%. 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 62.5% on time across 342 flights.

Southwest on STL to SFO did not run the same all year. Its best quarter was Jan–Mar 2026 at 81.5% on time and its weakest Apr–Jun 2026 at 31.7%, a swing of 50 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, Tuesday is the strongest day at 71.7% on time and Sunday the weakest at 56.9%. 15 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. National Airspace System accounts for 61% of the 7,399 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.

National Airspace System
61%
Late-arriving aircraft
19%
Carrier
16%
Extreme weather
4%

61% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 4,486 minutes out of 7,399, against a national NAS share of 21%. The split is drawn from 7,399 reported delay minutes.

Cancellations are rare at 0.29%, 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. 15.2% 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 49.0% on time across 342 flights, 14 points below 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 STL to SFO

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 62.5% 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