Route reliability record
STL→ATL
St. Louis to Atlanta
- Flights
- 3,705
- Period
- July 2025 to June 2026
- Distance
- 484 mi
- Carriers
- 3
This route earns a A. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 8 points better than the national rate of 77.6%. When something does go wrong the average delay runs a little over an hour. That rests on 3,705 flights, of which Delta Air Lines flew 2,371 at 89.4% on time.
Set against the rest of the country, this route's record is 8 points better than the US average of 77.6%. That gap is worth roughly 77 fewer late arrivals for every thousand flights.
Key figures
On time
85.3%
Arrivals under 15 minutes late, of 3,632 completed flights
Avg delay
72 min
Across delayed arrivals only, not all flights
Cancelled
1.73%
National rate is 1.81%
Best carrier
Delta
89.4% on time across 2,371 flights
These figures cover 3,705 flights between July 2025 and June 2026. The median arrival is 12 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Carrier by carrier
Which airline is most reliable on STL to ATL
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 89.4% of the time; Southwest Airlines manages 80.7%. Sample sizes sit next to every figure, because a two-point gap across 1,130 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 2,371 | 89.4% | 77 min | 1.98% | A |
| Southwest Airlines | 1,130 | 80.7% | 59 min | 1.15% | B |
| Frontier Airlinesthin sample | 204 | 62.8% | 92 min | 1.96% | D |
Delta leads Southwest by 9 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
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 27 points, against 9 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am765 flights93.5%
- 8am–11am796 flights93.4%
- 11am–2pm624 flights86.2%
- 2pm–5pm623 flights77.8%
- 5pm–8pm804 flights76.6%
- 8pm–5am93 flights66.7%
Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 93.5% of the time, against 66.7% for the overnight window. That is 27 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 804 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 17 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.
September is the best month on the calendar at 95.0% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. July was the busiest month here, with 351 flights.
Across the week, Wednesday is the strongest day at 91.9% on time and Monday the weakest at 80.3%. 12 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 45% of the 38,000 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.
- 45%Late-arriving aircraft
- 34%Carrier
- 15%National Airspace System
- 6%Extreme weather
45% 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 38,000 reported delay minutes here, that single category outweighs weather by 8 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 38,263 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 93.5% on time here.
Cancellations sit at 1.73% against a national 1.81%, which is ordinary. Diversions add another 0.24%.
Connections and stage length
What a delay here actually costs
5.1% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route are the a little over an hour kind, which a normal layover absorbs.
At 484 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 5am–8am window matters as much as it does.
The return leg runs 82.4% on time across 3,706 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.
The sample behind these figures is 3,705 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 95.0% on time and March 78.5%, a swing of 17 points. If the dates move at all, move them out of March before you think about anything else. 3,632 completed flights over 12 months sit behind that.
Common questions
STL to ATL questions
How often is STL to ATL delayed?
About one flight in seven arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 14.7% of the 3,705 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.
Which airline is most reliable on STL to ATL?
Delta Air Lines leads at 89.4% on time across 2,371 flights. Southwest Airlines is at the other end on 80.7%, a gap of 9 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on STL to ATL?
The 5am–8am departure window is the strongest at 93.5% on time. The 8pm–5am window is the weakest at 66.7%, 27 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 March delays on STL to ATL?
March is the weakest month at 78.5% on time, compared with 95.0% in September. Across the year that is 17 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
- ATL to STL — the return legseparate record
- St. Louis Lambert International (STL) delay statistics
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Delta Air Lines on-time record89.4%
- Southwest Airlines on-time record80.7%
- Frontier Airlines on-time record62.8%
- 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. STL to ATL and ATL to STL are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.