Route reliability record
BOS→STL
Boston to St. Louis
- Flights
- 1,611
- Period
- July 2025 to June 2026
- Distance
- 1,047 mi
- Carriers
- 3
This route lands a B, about a point worse than the national rate of 77.6%. About one flight in four arrives 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 1,611 BOS to STL flights, of which Envoy Air flew 418 at 82.2% on time.
Best time to fly BOS to STL: a 5am–8am departure, ideally on a Saturday. Flights in that window arrived on time 93.5% of the time and Saturday flights 83.8%, against 76.5% for the route overall.
The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
76.5%
Arrivals under 15 minutes late, of 1,582 completed flights
Avg delay
63 min
Across delayed arrivals only, not all flights
Cancelled
1.37%
National rate is 1.81%
Best carrier
Envoy
82.2% on time across 418 flights
These figures cover 1,611 flights between July 2025 and June 2026. Beyond the headline rate, 8.3% 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 BOS to STL
The choice of carrier is not cosmetic here. Envoy Air arrives on time 82.2% of the time; Southwest Airlines manages 72.4%. Sample sizes sit next to every figure, because a two-point gap across 935 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Republic Airwaysthin sample | 258 | 82.3% | 49 min | 3.10% | B− |
| Envoy Air | 418 | 82.2% | 74 min | 1.20% | B |
| Southwest Airlines | 935 | 72.4% | 62 min | 0.96% | C+ |
Envoy leads Southwest by 10 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Best ways to make this trip
The most reliable ways to fly Boston to St. Louis
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. BOS → STLBoston to St. Louis | Envoy Air | 81.2% | 82.2% | 1.20% | 5am–8am, Sat | — |
| 2. BOS → STLBoston to St. Louis | Southwest Airlines | 71.7% | 72.4% | 0.96% | 5am–8am, Sat | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 45 points, against 10 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am593 flights93.5%
- 8am–11am151 flights85.7%
- 11am–2pm237 flights78.5%
- 2pm–5pm296 flights67.4%
- 5pm–8pm320 flights48.4%
- 8pm–5am14 flights—
Scale runs 40% to 100%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 48.4% on time, against 93.5% 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 5am–8am window is the busiest, with 593 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 23 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 October, when the on-time rate falls to 64.9%. January is the strongest month at 87.5%. Moving a flexible trip across that boundary buys 23 points. October was the busiest month here, with 150 flights.
Across the week, Saturday is the strongest day at 83.8% on time and Sunday the weakest at 68.1%. 16 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 62% of the 23,000 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.
- 62%Late-arriving aircraft
- 23%Carrier
- 11%National Airspace System
- 4%Extreme weather
62% 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 23,000 reported delay minutes here, that single category outweighs weather by 17 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 23,331 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 1.37% against a national 1.81%, which is ordinary. Diversions add another 0.43%.
Connections and stage length
What a delay here actually costs
8.3% 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 last about an hour, which a normal layover absorbs.
The 1,047 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg is a different operation and performs like one: it runs 70.3% on time across 1,610 flights, 6 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 6 points of difference.
The sample behind these figures is 1,611 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.
Work out the risk of missing a connection in STL after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 87.5% on time and October 64.9%, a swing of 23 points. If the dates move at all, move them out of October before you think about anything else. 1,582 completed flights over 12 months sit behind that.
Common questions
BOS to STL questions
How often is BOS to STL delayed?
About one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 23.5% of the 1,611 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on BOS to STL?
Envoy Air leads at 82.2% on time across 418 flights. Southwest Airlines is at the other end on 72.4%, a gap of 10 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 BOS to STL?
The 5am–8am departure window is the strongest at 93.5% on time. The 5pm–8pm window is the weakest at 48.4%, 45 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 October delays on BOS to STL?
October is the weakest month at 64.9% on time, compared with 87.5% in January. Across the year that is 23 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 BOS — the return legseparate record
- Boston Logan International (BOS) delay statistics
- St. Louis Lambert International (STL) delay statistics
- Republic Airways on BOS to STL82.3%
- Envoy Air on BOS to STL82.2%
- Southwest Airlines on BOS to STL72.4%
- BOS to DCA, a related route74.0%
- ATL to STL, a related route82.4%
- BOS to ORD, a related route72.7%
- Republic Airways on-time record82.3%
- Envoy Air on-time record82.2%
- Southwest Airlines on-time record72.4%
- 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. BOS to STL and STL to BOS 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.