Route reliability record

ATL→STL

Atlanta to St. Louis

Flights: 3,706
Period: July 2025 to June 2026
Distance: 484 mi
Carriers: 3

This route lands a B, 5 points better than the national rate of 77.6%. About one flight in six arrive 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 3,706 flights, of which Delta Air Lines flew 2,371 at 84.7% on time.

Set against the rest of the country, this route's record is 5 points better than the US average of 77.6%. That gap is worth roughly 48 fewer late arrivals for every thousand flights.

On time

82.4%

Arrivals under 15 minutes late, of 3,642 completed flights

Avg delay

56 min

Across delayed arrivals only, not all flights

Cancelled

1.54%

National rate is 1.81%

Best carrier

Delta

84.7% on time across 2,371 flights

These figures cover 3,706 flights between July 2025 and June 2026. The median arrival is 7 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 ATL to STL

The two carriers here are closely matched: 5 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

On-time performance by carrier on ATL to STL
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	2,371	84.7%	55 min	1.98%	B
Southwest Airlines	1,130	79.9%	56 min	0.53%	B+
Frontier Airlinesthin sample	205	69.7%	57 min	1.95%	C

No carrier stands out. Delta tops the table at 84.7%, 5 points clear of the bottom, which is inside the range this kind of sample moves year to year.

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 20 points, against 5 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am336 flights92.2%
8am–11am786 flights88.2%
11am–2pm525 flights84.6%
2pm–5pm740 flights83.1%
5pm–8pm540 flights78.8%
8pm–5am779 flights72.6%

Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 92.2% of the time, against 72.6% for the overnight window. That is 20 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 786 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 16 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.

Darker means more delays. Figures are on-time percentages.September best, March worst

September is the best month on the calendar at 92.4% 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 89.4% on time and Sunday the weakest at 75.5%. 14 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. Carrier accounts for 44% of the 36,000 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.

Carrier
44%
Late-arriving aircraft
41%
National Airspace System
11%
Extreme weather
4%
Security
1%

41% 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 36,000 reported delay minutes here, that single category outweighs weather by 10 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 35,727 reported delay minutes.

The largest share of delay minutes, 44%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 16,000 of the 36,000 delay minutes reported here.

Cancellations sit at 1.54% against a national 1.81%, which is ordinary. Diversions add another 0.19%.

Connections and stage length

What a delay here actually costs

5.2% 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 about 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 85.3% on time across 3,705 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 3,706 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 92.4% on time and March 76.7%, a swing of 16 points. If the dates move at all, move them out of March before you think about anything else. 3,642 completed flights over 12 months sit behind that.

Common questions

ATL to STL questions

How often is ATL to STL delayed?

About one flight in six arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 17.6% of the 3,706 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on ATL to STL?

Delta Air Lines leads at 84.7% on time across 2,371 flights. Southwest Airlines is at the other end on 79.9%, a gap of 5 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 ATL to STL?

The 5am–8am departure window is the strongest at 92.2% on time. The 8pm–5am window is the weakest at 72.6%, 20 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 ATL to STL?

March is the weakest month at 76.7% on time, compared with 92.4% in September. Across the year that is 16 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. ATL to STL and STL to ATL 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.

Key figures