Route profile
BOS→SJU
Flight reliability, delays and best times to fly from Boston to San Juan, 1,674 miles.
Right now
Aviation weather is not currently a factor.
Aviation weather is not currently a factor.
Route reliability
July 2023 – July 2026
Better than 5% of comparable major US routes (4,598 compared)
Calculated from 5,995 flights. How this is calculated
BOS → SJU arrives on time 67.7% of the time; the return trip, SJU → BOS, arrives on time 73.0% of the time, a 5.3-point gap between the two directions of the same city pair.
BOS → SJU spends 26.5 minutes on the ground on a 1,674-mile trip: 20.3 minutes from pushback to wheels-up at BOS and 6.2 minutes from touchdown to gate at SJU.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
What stands out
The airline matters unusually much on this route, a wider carrier-to-carrier gap than 100% of 2,692 comparable routes.
Delta Air Lines arrived on time 79.3% of the time, against 42.7% for Frontier Airlines, flying the exact same route.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Ranked against every other route with the same kind of figure and at least 2,692 in the comparison.
Why BOS → SJU flights are cancelled
July 2023 – July 2026
BOS → SJU cancelled 102 of 5,995 scheduled flights — about 1 in every 59. The reason filed most often was extreme weather, 38.2% of the cancellations coded on this route — about 1 in every 154 scheduled flights.
Share of cancellations
Of 102 cancelled departures carrying a reason code.
What each reason means
Conditions the carrier judged severe enough to stop the flight: a blizzard, a hurricane, a line of thunderstorms.
39 cancellations, 38.2% of the total.
Crew, maintenance, aircraft cleaning, baggage or fueling: what BTS counts as within the carrier’s own control.
35 cancellations, 34.3% of the total.
Airport capacity, air traffic control flow programs, heavy traffic and ordinary bad weather. A system decision, not the airline’s.
26 cancellations, 25.5% of the total.
A terminal evacuation, a security breach, screening equipment failure, or screening queues over 29 minutes.
2 cancellations, 2.0% of the total.
Reason codes are the operating airline’s own filing with US DOT, not an independent finding of fault. Ordinary bad weather is filed under air traffic, so weather’s full share is larger than its bar.
102 coded cancellations were recorded on BOS → SJU; the section appears from 50.
When it goes wrong
July 2023 – July 2026
73 min late
against a median of 0 min early
BOS → SJU has an average that understates its risk: a typical arrival is 0 min early, but the worst tenth are 73 minutes worse than that. If the trip has something unmissable at the end of it, the median is the wrong number to plan against.
Percentiles over 5,995 operations; cancelled and diverted flights are counted separately.
Will your connection be tight enough?
Layovers at SJU after arriving from BOS.
| Connection time | Chance of missing | Reads as |
|---|---|---|
| 30 min | 49% | Likely to miss |
| 45 min | 32% | Likely to miss |
| 60 min | 22% | High risk |
| 90 min | 12% | Some risk |
| 120 min | 7.5% | Some risk |
This is one leg of a connection. Gate changes and the next flight's own schedule matter too. And a connection can fail before delay is even the question — this route cancels 1.70% of the time and diverts 0.27% of the time, which a late arrival never shows up in.
Chance of missing is the share of 5,877 arrivals on this route that landed later than the connection time less 30 minutes to reach the next gate.
The worst tenth of arrivals on this route land at least 73 minutes late (90th-percentile gate arrival delay), over 5,995 operations.
Any other layover length: connection checker.
Best time to fly
BOS → SJU flights departing 5–9 AM arrived on time 79.1% of the time, against 54.2% for 9 PM–5 AM departures, a gap of 24.9 percentage points.
By departure window
By departure hour
- 12 AM to 5 AM: too few flights to score
- 6 AM: 72.7% on time from 325 flights
- 7 AM: 80.3% on time from 529 flights
- 8 AM: 80.3% on time from 1,169 flights
- 9 AM: 67.1% on time from 213 flights
- 10 AM: 63.4% on time from 543 flights
- 11 AM: 56.3% on time from 331 flights
- 12 PM: 65.1% on time from 597 flights
- 1 PM: 58.0% on time from 288 flights
- 2 PM: 60.9% on time from 239 flights
- 3 PM: 66.3% on time from 209 flights
- 4 PM: 57.7% on time from 124 flights
- 5 PM: 63.9% on time from 127 flights
- 6 PM: 61.1% on time from 165 flights
- 7 PM: 63.1% on time from 304 flights
- 8 PM: 63.5% on time from 279 flights
- 9 PM: too few flights to score
- 10 PM: 58.7% on time from 297 flights
- 11 PM: too few flights to score
Why BOS → SJU runs late
July 2023 – July 2026
crew, maintenance, boarding and fueling, all within the carrier’s control
the inbound aircraft was late, so this flight started late
airspace and airport capacity, including weather-driven flow control
weather severe enough to stop this flight specifically
screening or terminal security incidents
Share of the delay minutes US DOT attributed to each cause for BOS → SJU. Only delays of 15 minutes or more are attributed.
Airlines on this route
Carriers with at least 200 flights, by the airline that operated each one.
| Carrier | Flights | On time | Cancelled | Median delay | Severe |
|---|---|---|---|---|---|
| JetBlue | 3,865 | 67.6% | 1.50% | 0 min | 12.7% |
| Delta Air Lines | 1,207 | 79.3% | 0.66% | -7 min | 5.1% |
| Spirit Airlines | 683 | 55.6% | 4.25% | 8 min | 18.1% |
| Frontier Airlines | 240 | 42.7% | 2.92% | 22 min | 26.0% |
JetBlue flew 64.5% of the 5,995 flights listed. Spirit Airlines cancelled 4.25% of its flights here against 0.66% for Delta Air Lines.
Delta Air Lines arrived on time 36.6 percentage points more often than Frontier Airlines on this route.
Flights on this route
Flight numbers with at least 600 operations here and still on the schedule.
DL1780 (8:10 AM) arrived on time 80.2% of the time, 16.9 points more often than B6561 (8:45 PM) at 63.3%.
Weekly and seasonal patterns
By day of week
Wednesday is historically the most reliable day and Sunday the least, a gap of 5.0 percentage points.
By month
- Jan: 63.7%
- Feb: 58.3%
- Mar: 69.5%
- Apr: 72.8%
- May: 76.2%
- Jun: 73.3%
- Jul: 65.1%
- Aug: 62.0%
- Sep: 75.7%
- Oct: 73.1%
- Nov: 69.8%
- Dec: 59.4%
February is historically the weakest month and May the strongest, a spread of 17.9 percentage points.
Reliability over time
July 2023 – July 2026
- July 2023: 52.9% from 176 flights
- August 2023: 60.9% from 177 flights
- September 2023: too few flights to score (118)
- October 2023: 72.3% from 144 flights
- November 2023: 72.0% from 157 flights
- December 2023: 67.5% from 155 flights
- January 2024: 66.5% from 156 flights
- February 2024: 60.8% from 156 flights
- March 2024: 71.0% from 163 flights
- April 2024: 77.4% from 171 flights
- May 2024: 74.2% from 162 flights
- June 2024: 67.9% from 212 flights
- July 2024: 65.5% from 230 flights
- August 2024: 53.7% from 222 flights
- September 2024: too few flights to score (117)
- October 2024: too few flights to score (116)
- November 2024: 64.9% from 150 flights
- December 2024: 53.5% from 185 flights
- January 2025: 65.3% from 180 flights
- February 2025: 58.5% from 187 flights
- March 2025: 70.3% from 212 flights
- April 2025: 69.6% from 193 flights
- May 2025: 76.2% from 151 flights
- June 2025: 80.6% from 160 flights
- July 2025: 80.0% from 175 flights
- August 2025: 73.0% from 181 flights
- September 2025: too few flights to score (83)
- October 2025: too few flights to score (95)
- November 2025: too few flights to score (110)
- December 2025: 58.6% from 170 flights
- January 2026: 58.9% from 170 flights
- February 2026: 55.8% from 178 flights
- March 2026: 67.5% from 204 flights
- April 2026: 72.0% from 187 flights
- May 2026: 78.6% from 140 flights
- June 2026: 73.0% from 126 flights
- July 2026: 60.2% from 126 flights
Over the most recent 12 months (2025-08 to 2026-07), on-time arrivals averaged 67.2% against 68.1% in the 12 months before — broadly unchanged.
Data and methodology
Calculated by FlyerIntel from 5,995 BOS → SJU flight records from the US DOT Bureau of Transportation Statistics, covering July 2023 – July 2026. Late means 15 or more minutes past scheduled arrival; cancelled and diverted flights are left out of on-time rates.
Full methodology · Data sources · Report a problem
Related research: How Long a Layover Needs to Be · Two Airlines on One Route · Best Time of Day to Fly From Major US Airports
Analysis last recomputed