Route on-time record
STL to BOS: most on-time flights and the best time to fly
St Louis (St. Louis Lambert International Airport) to Boston (Boston Logan International Airport). 1,612 nonstop flights in Jun 2025 to May 2026, 71% arrived within 15 minutes and 1.5% were cancelled. The most reliable flight number was Southwest 3948 at 10:15 AM.
Flying on a specific date? We’ll adjust for the month, the weekday and the forecast.
STL → BOS
St Louis to Boston: 1,612 nonstop flights a year
On time (12 months)
71%
Cancelled
1.5%
avg delay 20 min
Best time to leave
Before 9 AM
91% on time vs 61% 6 to 9 PM
Most reliable airline
Republic
74% chance on time
Lowest nonstop fare seen in the next two months: $303 (Southwest 4527 on 2026-10-24). Fares open on our travel partner (Aviasales). Pick the flight number you chose here.
Most reliable nonstop flights
Ranked by the chance the flight operates and arrives within 15 minutes of schedule, from Jun 2025 to May 2026 records.
#1 · Southwest 3948
10:15 AM → 1:50 PM2h 35m nonstop
Local times, typical schedule. Last flown 2026-05-31.
81%
chance on time
- On time (history)
- 83%
- Cancelled
- 0.0%
- Avg arrival delay
- 12 min
- Arrived on time 83% of the time (46 flights, Jun 2025 to May 2026).
- Never cancelled in 46 scheduled flights.
- Lands inside BOS's trouble window: 79% of its 196 ground stops and delay programs started between noon and 6 PM.
Limited track record · 46 flights
Find Southwest 3948 fares Opens this date on Aviasales#2 · Southwest 454
10:35 AM → 2:10 PM2h 35m nonstop
Local times, typical schedule. Last flown 2026-05-30.
78%
chance on time
- On time (history)
- 75%
- Cancelled
- 0.0%
- Avg arrival delay
- 6 min
- Arrived on time 75% of the time (8 flights, Jun 2025 to May 2026).
- Lands inside BOS's trouble window: 79% of its 196 ground stops and delay programs started between noon and 6 PM.
Limited track record · 8 flights
Find Southwest 454 fares Opens this date on Aviasales#3 · Republic 4624 · sold as American Eagle, Delta Connection or United Express
11:45 AM → 3:31 PM2h 46m nonstop
Local times, typical schedule. Last flown 2026-05-20.
76%
chance on time
- On time (history)
- 74%
- Cancelled
- 0.0%
- Avg arrival delay
- 27 min
- Arrived on time 74% of the time (43 flights, Jun 2025 to May 2026).
- Never cancelled in 43 scheduled flights.
- Lands inside BOS's trouble window: 79% of its 196 ground stops and delay programs started between noon and 6 PM.
- 58% of its delay minutes came from the plane arriving late from an earlier flight.
Limited track record · 43 flights
Find 11:45 AM flight fares Opens this date on Aviasales#4 · Envoy 4224 · sold as American Eagle
5:49 PM → 9:30 PM2h 41m nonstop
Local times, typical schedule. Last flown 2026-05-20.
70%
chance on time
- On time (history)
- 67%
- Cancelled
- 0.0%
- Avg arrival delay
- 35 min
- Arrived on time 67% of the time (43 flights, Jun 2025 to May 2026).
- Never cancelled in 43 scheduled flights.
Limited track record · 43 flights
Find 5:49 PM flight fares Opens this date on Aviasales#5 · Republic 4678 · sold as American Eagle, Delta Connection or United Express
7:51 PM → 11:36 PM2h 45m nonstop
Local times, typical schedule. Last flown 2026-05-31.
64%
chance on time
- On time (history)
- 60%
- Cancelled
- 0.0%
- Avg arrival delay
- 14 min
- Arrived on time 60% of the time (10 flights, Jun 2025 to May 2026).
- Leaves in this route's least on-time window (6 to 9 PM: 61% on time; Before 9 AM: 91%).
- 94% of its delay minutes came from the plane arriving late from an earlier flight.
Limited track record · 10 flights
Find 7:51 PM flight fares Opens this date on Aviasales#6 · Southwest 4438
2:30 PM → 6:05 PM2h 35m nonstop
Local times, typical schedule. Last flown 2026-05-31.
60%
chance on time
- On time (history)
- 58%
- Cancelled
- 0.0%
- Avg arrival delay
- 20 min
- Arrived on time 58% of the time (38 flights, Jun 2025 to May 2026).
- Never cancelled in 38 scheduled flights.
Limited track record · 38 flights
Find Southwest 4438 fares Opens this date on Aviasales#7 · Southwest 4439
7:40 PM → 11:10 PM2h 30m nonstop
Local times, typical schedule. Last flown 2026-05-31.
53%
chance on time
- On time (history)
- 49%
- Cancelled
- 0.0%
- Avg arrival delay
- 37 min
- Arrived on time 49% of the time (55 flights, Jun 2025 to May 2026).
- Never cancelled in 55 scheduled flights.
- Leaves in this route's least on-time window (6 to 9 PM: 61% on time; Before 9 AM: 91%).
- 63% of its delay minutes came from the plane arriving late from an earlier flight.
Limited track record · 55 flights
Find Southwest 4439 fares Opens this date on Aviasales
Airlines on this route
Season-adjusted chance of operating and arriving on time.
- Republic Airways (sold as American Eagle, Delta Connection or United Express)74%
228 flights · 78% on time as flown · 2.4% cancel
- Envoy Air (sold as American Eagle)73%
448 flights · 75% on time as flown · 1.7% cancel
- Southwest Airlines67%
936 flights · 67% on time as flown · 1.0% cancel
On time by departure time
All airlines, scheduled local departure, Jun 2025 to May 2026.
- Before 9 AM91%
223 flights · avg delay 6 min
- 9 AM to noon82%
400 flights · avg delay 13 min
- Noon to 3 PM63%
361 flights · avg delay 24 min
- 3 to 6 PM61%
176 flights · avg delay 29 min
- 6 to 9 PM61%
443 flights · avg delay 28 min
Best day: Tuesday (79%). Worst: Thursday (69%).
On time by month
All airlines, Jun 2023 to May 2026. Several years per month, so one stormy season doesn't define a month. Travel-month estimates use this seasonal pattern.
What delays this route
- Late-arriving aircraft47%
- Air traffic control and airport volume29%
- Airline (crew, maintenance, boarding)21%
- Severe weather2%
Share of delay minutes by the cause airlines report to the US DOT.
Historical odds, not a guarantee. Built from the US DOT Bureau of Transportation Statistics on-time reports (Jun 2025 to May 2026), FAA ground stop and delay program advisories, and 20 years of airport weather observations. Covers US airlines that report to the DOT; schedules are flights operated recently, so confirm times when you book. ATIS Alerts is not affiliated with any airline. Fares are what Aviasales travelers saw in recent searches (USD, one way, 1 adult), not live quotes; the partner site shows the current price. Fare links go to our travel partner and may earn us a commission at no cost to you. Affiliate disclosure
STL to BOS questions
- What time of day is best to fly STL to BOS?
- Before 9 AM: 91% of flights arrived on time, against 61% for departures 6 to 9 PM. Later flights inherit delays from earlier ones, so the first departures of the day usually run best.
- Which airline is most on time from STL to BOS?
- Republic, with a season-adjusted 74% chance of operating and arriving on time over 228 flights. The adjustment compares each airline with what the route did in the months it flew, so a carrier that skipped a stormy month gets no free credit.
- What is the worst month for delays on STL to BOS?
- July (66% on time); the best was February (84%), averaged over Jun 2023 to May 2026.
- Is this a prediction for my flight?
- No. These are historical odds from the US DOT on-time reports, FAA advisories and airport weather records. Check your flight status and the FAA delay board on the day you fly.
More routes from STL
- BOS to STL (return)
- STL to ATL 85%
- STL to DEN 75%
- STL to ORD 71%
- STL to LGA 75%
- STL to MCO 78%
- STL to DCA 73%
- STL to DFW 74%
- STL to PHX 76%
- STL to LAS 79%
- STL to DAL 77%
- STL to DTW 83%
- STL to MSP 80%
Most on-time flights from STL on every route →
Live status: FAA delays and ground stops