Route reliability record
STL→SFO
St. Louis to San Francisco
- Flights
- 782
- Period
- July 2025 to June 2026
- Distance
- 1,735 mi
- Carriers
- 3
This route draws a D+. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is a little over an hour behind schedule. Build slack into anything you connect to. That rests on 782 STL to SFO flights, with a median arrival 4 minutes late.
Best time to fly STL to SFO: a 11am–2pm departure, ideally on a Tuesday. Flights in that window arrived on time 75.0% of the time and Tuesday flights 72.9%, against 63.0% for the route overall.
The national on-time rate over the same period is 77.6%, so this route runs 15 points behind the country as a whole. Across a thousand flights that is about 146 extra late arrivals.
Key figures
On time
63.0%
Arrivals under 15 minutes late, of 775 completed flights
Avg delay
72 min
Across delayed arrivals only, not all flights
Cancelled
0.90%
National rate is 1.81%
Best carrier
—
No carrier clears the floor
These figures cover 782 flights between July 2025 and June 2026. Beyond the headline rate, 16.3% 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
Which airline is most reliable on STL to SFO
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 |
|---|---|---|---|---|---|
| United Airlinesthin sample | 207 | 63.6% | 68 min | 0.48% | D+ |
| SkyWest Airlinesthin sample | 233 | 63.2% | 96 min | 2.15% | D |
| Southwest Airlinesthin sample | 342 | 62.5% | 58 min | 0.29% | D+ |
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 14 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–8am87 flights66.3%
- 8am–11am283 flights60.9%
- 11am–2pm80 flights75.0%
- 2pm–5pm7 flights—
- 5pm–8pm325 flights61.4%
- 8pm–5am—
Scale runs 50% 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 60.9%. 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 5pm–8pm window is the busiest, with 325 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 70 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
June is the worst month at 18.3% on time, 70 points below January, the best at 88.1%. 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. July was the busiest month here, with 83 flights.
Across the week, Tuesday is the strongest day at 72.9% on time and Monday the weakest at 57.5%. 15 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. National Airspace System accounts for 50% of the 21,000 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.
- 50%National Airspace System
- 28%Carrier
- 19%Late-arriving aircraft
- 3%Extreme weather
- 0%Security
50% 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 10,000 minutes out of 21,000, against a national NAS share of 21%. The split is drawn from 20,534 reported delay minutes.
Cancellations sit at 0.90% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here actually costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 16.3% 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 runs 65.8% on time across 781 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. 782 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.
Work out the risk of missing a connection in SFO after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 782 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 63.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 775 completed flights over 12 months sit behind that.
Common questions
STL to SFO questions
How often is STL to SFO delayed?
Roughly one flight in three arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 37.0% of the 782 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.
How reliable is STL to SFO compared with the rest of the country?
63.0% of flights arrive on time here against a national 77.6%, a difference of 15 points against it. That is worth a D+ on this site's grading scale.
What time of day has the fewest delays on STL to SFO?
The 11am–2pm departure window is the strongest at 75.0% on time. The 8am–11am window is the weakest at 60.9%, 14 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are June delays on STL to SFO?
June is the weakest month at 18.3% on time, compared with 88.1% in January. Across the year that is 70 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- SFO to STL — the return legseparate record
- St. Louis Lambert International (STL) delay statistics
- San Francisco International (SFO) delay statistics
- United Airlines on STL to SFO63.6%
- SkyWest Airlines on STL to SFO63.2%
- Southwest Airlines on STL to SFO62.5%
- STL to ATL, a related route85.3%
- LAX to SFO, a related route64.8%
- STL to DEN, a related route74.9%
- United Airlines on-time record63.6%
- SkyWest Airlines on-time record63.2%
- Southwest Airlines on-time record62.5%
- The best time of day to fly, according to 7.04 million flight records
- How often a connection fails at the major US hubs
Direction matters. STL to SFO and SFO to STL are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.