Route reliability record
ORD→STL
Chicago to St. Louis
- Flights
- 3,068
- Period
- July 2025 to June 2026
- Distance
- 258 mi
- Carriers
- 5
This route sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 7 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 3,068 flights, of which Republic Airways flew 444 at 76.2% on time.
Republic Airways is the most reliable of the five carriers covered here at 76.2% on time across 444 flights.
Key figures
On time
71.0%
Arrivals under 15 minutes late, of 2,977 completed flights
Avg delay
73 min
Across delayed arrivals only, not all flights
Cancelled
2.74%
National rate is 1.81%
Best carrier
Republic
76.2% on time across 444 flights
These figures cover 3,068 flights between July 2025 and June 2026. Beyond the headline rate, 11.4% 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 ORD to STL
The choice of carrier is not cosmetic here. Republic Airways arrives on time 76.2% of the time; American Airlines manages 65.6%. Sample sizes sit next to every figure, because a two-point gap across 535 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Republic Airways | 444 | 76.2% | 77 min | 2.48% | B |
| Envoy Air | 727 | 75.0% | 52 min | 2.34% | B |
| United Airlines | 528 | 71.2% | 79 min | 1.33% | C |
| SkyWest Airlines | 834 | 68.2% | 73 min | 4.20% | C− |
| American Airlines | 535 | 65.6% | 86 min | 2.62% | C |
SkyWest Airlines cancels 4.2% of what it schedules here, the highest in the table. A cancelled flight never appears in an on-time rate, so read that column alongside the punctuality one rather than after 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 22 points, against 11 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am315 flights81.0%
- 8am–11am272 flights73.2%
- 11am–2pm707 flights78.2%
- 2pm–5pm758 flights72.9%
- 5pm–8pm564 flights62.6%
- 8pm–5am452 flights58.8%
Scale runs 50% to 85%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 58.8% on time, against 81.0% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 2pm–5pm window is the busiest, with 758 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 24 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.
December is the weak month at 59.1% on time, against 83.6% in September. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. May was the busiest month here, with 324 flights.
Across the week, Tuesday is the strongest day at 76.4% on time and Sunday the weakest at 65.3%. 11 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 43% of the 63,000 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.
- 43%Late-arriving aircraft
- 32%Carrier
- 13%National Airspace System
- 11%Extreme weather
Extreme weather accounts for 11% of delay minutes, well above the single-digit share typical across the system. Weather delays are lumpy: they arrive as whole bad days rather than as a steady drag, so the monthly strip above is the more useful view of the risk. The national share is 6%, so this operation carries roughly 1.8 times the usual weather exposure. The split is drawn from 62,814 reported delay minutes.
43% 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 63,000 reported delay minutes here, that single category outweighs weather by 4 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.
Cancellations run at 2.74%, against 1.81% nationally. That is roughly one flight in 40 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.
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. 11.4% 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 258 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 71.1% on time across 3,070 flights, within half a point 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 3,068 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 83.6% on time and December 59.1%, a swing of 24 points. If the dates move at all, move them out of December before you think about anything else. 2,977 completed flights over 12 months sit behind that.
Common questions
ORD to STL questions
How often is ORD to STL delayed?
Roughly one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 29.0% of the 3,068 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 ORD to STL?
Republic Airways leads at 76.2% on time across 444 flights. American Airlines is at the other end on 65.6%, a gap of 11 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 ORD to STL?
The 5am–8am departure window is the strongest at 81.0% on time. The 8pm–5am window is the weakest at 58.8%, 22 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 December delays on ORD to STL?
December is the weakest month at 59.1% on time, compared with 83.6% in September. Across the year that is 24 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 ORD — the return legseparate record
- Chicago O'Hare International (ORD) delay statistics
- St. Louis Lambert International (STL) delay statistics
- Republic Airways on-time record76.2%
- Envoy Air on-time record75.0%
- United Airlines on-time record71.2%
- Why the first flight of the morning is statistically safest
- What a cancellation rate actually tells you (and what it hides)
Direction matters. ORD to STL and STL to ORD 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.