Route reliability record
SFO→STL
San Francisco to St. Louis
- Flights
- 781
- Period
- July 2025 to June 2026
- Distance
- 1,735 mi
- Carriers
- 3
This route draws a C+. About 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 781 SFO to STL flights, with a median arrival 1 minute late.
Best time to fly SFO to STL: a 2pm–5pm departure, ideally on a Saturday. Flights in that window arrived on time 76.3% of the time and Saturday flights 78.2%, against 65.8% for the route overall.
The national on-time rate over the same period is 77.6%, so this route runs 12 points behind the country as a whole. Across a thousand flights that is about 118 extra late arrivals.
Key figures
On time
65.8%
Arrivals under 15 minutes late, of 771 completed flights
Avg delay
63 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 781 flights between July 2025 and June 2026. Beyond the headline rate, 12.7% 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 SFO to STL
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 | 204 | 80.7% | 52 min | 0.49% | B+ |
| SkyWest Airlinesthin sample | 235 | 77.6% | 85 min | 2.55% | B |
| Southwest Airlinesthin sample | 342 | 49.0% | 59 min | 0.00% | F+ |
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 19 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–11am299 flights71.6%
- 11am–2pm355 flights57.8%
- 2pm–5pm41 flights76.3%
- 5pm–8pm—
- 8pm–5am73 flights70.4%
Scale runs 50% to 80%. 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 57.8% on time against 76.3% for 2pm–5pm. 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 355 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 44 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.
Delays peak in May, when the on-time rate falls to 46.5%. January is the strongest month at 90.9%. Moving a flexible trip across that boundary buys 44 points. July was the busiest month here, with 83 flights.
Across the week, Saturday is the strongest day at 78.2% on time and Monday the weakest at 56.5%. 22 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. Late-arriving aircraft accounts for 57% of the 17,000 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.
- 57%Late-arriving aircraft
- 27%Carrier
- 16%National Airspace System
- 0%Extreme weather
57% 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 17,000 reported delay minutes here, that single category outweighs weather by 57 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 16,592 reported delay minutes.
Cancellations sit at 0.90% against a national 1.81%, which is ordinary. Diversions add another 0.38%.
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. 12.7% 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 63.0% on time across 782 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. 781 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 STL after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 781 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 65.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 771 completed flights over 12 months sit behind that.
Common questions
SFO to STL questions
How often is SFO to STL delayed?
About 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 34.2% of the 781 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is SFO to STL compared with the rest of the country?
65.8% of flights arrive on time here against a national 77.6%, a difference of 12 points against it. That is worth a C+ on this site's grading scale.
What time of day has the fewest delays on SFO to STL?
The 2pm–5pm departure window is the strongest at 76.3% on time. The 11am–2pm window is the weakest at 57.8%, 19 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 May delays on SFO to STL?
May is the weakest month at 46.5% on time, compared with 90.9% in January. Across the year that is 44 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
- STL to SFO — the return legseparate record
- San Francisco International (SFO) delay statistics
- St. Louis Lambert International (STL) delay statistics
- United Airlines on SFO to STL80.7%
- SkyWest Airlines on SFO to STL77.6%
- Southwest Airlines on SFO to STL49.0%
- SFO to LAX, a related route73.9%
- ATL to STL, a related route82.4%
- SFO to SEA, a related route73.7%
- United Airlines on-time record80.7%
- SkyWest Airlines on-time record77.6%
- Southwest Airlines on-time record49.0%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
Direction matters. SFO to STL and STL to SFO 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.