65% of flights from Boston to San Juan arrived on time over the past 12 months. That is worse than the typical U.S. route. The 8 a.m. departures ran on time 77% of the time; the 10 a.m. ones 55%. Most reliable airline: Delta Air Lines (73%). 15% of flights arrived more than an hour late or not at all.
How late?
The on-time rate treats a flight 20 minutes late the same as one 5 hours late. Here's the split for BOS → SJU: when a flight was late, it was under 45 minutes late 48% of the time. About 1 in 8 flights landed an hour or more late, and 1 in 37 three hours or more; 3.0% were cancelled outright.
- On time or early65%
- 15–30 min late8.8%
- 30–60 min late11%
- 1–2 hours late6.9%
- 2–3 hours late2.8%
- 3+ hours late2.7%
- Diverted0.1%
- Cancelled3.0%
Share of all 1,717 scheduled flights, past 12 months, by arrival time against schedule.
By airline
| Airline | Flights | On time | Cancelled | Typical arrival | 1h+ late | Avg when late | Operated by |
|---|---|---|---|---|---|---|---|
| JetBlue | 1,142 | 65% | 2.8% | +1 min | 13.1% | +73 min | JetBlue |
| Delta Air Lines | 398 | 73% | 1.5% | −4 min | 6.0% | +57 min | Delta Air Lines |
| Spirit Airlines | 143 | 48% | 8.4% | +11 min | 19.6% | +108 min | Spirit Airlines |
| Frontier Airlines | 34 | — | — | — | — | — | Frontier Airlines |
Airline = the name on the ticket. Regional flights (e.g. "Delta Connection") count under the ticketing airline, and the operator is listed.
Best time of day to fly
On-time rate by scheduled departure hour (local time at BOS). Delays build through the day as late planes knock on, so early flights usually do best.
By airline and hour
| Departs | JetBlue | Delta Air Lines |
|---|---|---|
| 8 a.m. | 83% | 76% |
| noon | 70% | — |
| 6 p.m. | 57% | — |
Last flight of the day
On BOS → SJU, each airline's last flight of the day was cancelled 3.2% of the time, against 3.1% for its earlier flights, about the same. It arrived 3+ hours late 3.7% of the time (earlier flights: 2.1%). It matters more than the numbers suggest. Miss an earlier flight and there's another one that evening; miss the last one and you're usually waiting until morning.
| Airline | Last departure | Last: cancelled | Last: 3h+ late | Earlier: cancelled | Next morning |
|---|---|---|---|---|---|
| JetBlue | 7:50 p.m. | 2.6% | 3.1% | 3.0% | first flight 6:00 a.m. |
Last flight = the airline's last scheduled departure on this route that day, on days it flies the route at least twice; past 12 months. Times are typical scheduled times over the latest three months.
By month
Each calendar month pooled over 2023–2026. Best: May (76%). Worst: February (56%).
By day of week
| Day | Flights | On time | Cancelled |
|---|---|---|---|
| Monday | 255 | 62% | 6.7% |
| Tuesday | 232 | 69% | 2.6% |
| Wednesday | 228 | 68% | 2.2% |
| Thursday | 252 | 62% | 0.8% |
| Friday | 244 | 67% | 0.8% |
| Saturday | 252 | 63% | 4.4% |
| Sunday | 254 | 62% | 3.1% |
Why flights were late
Share of delay minutes on flights 15+ minutes late, as reported to BTS by the airlines.
Cancellations: weather 20 · airline 16 · air traffic/airport 13 · security 2
Month by month
Flight numbers on this route
Regular flights with at least 120 scheduled trips in the past year. Sorted by departure time.
| Flight | Departs | Flights | On time | Cancelled | Typical arrival | Operated by |
|---|---|---|---|---|---|---|
| B6 861 | 8:00 a.m. | 364 | 71% | 2.5% | −5 min | JetBlue |
| DL 1780 | 8:05 a.m. | 365 | 76% | 1.1% | −4 min | Delta Air Lines |
| B6 561 | 6:45 p.m. | 274 | 47% | 3.6% | +17 min | JetBlue |
Worst days in the past year
| Date | Flights | On time | Cancelled |
|---|---|---|---|
| Jan 4, 2026 | 9 | 0% | 0 |
| Feb 21, 2026 | 8 | 0% | 0 |
| Feb 23, 2026 | 8 | 0% | 8 |
| Jan 3, 2026 | 7 | 0% | 7 |
| Feb 7, 2026 | 6 | 0% | 0 |
Questions
How often are flights from BOS to SJU on time?
65% of 1,717 scheduled flights from Boston, MA to San Juan, PR arrived within 15 minutes of schedule between September 2025 and August 2026. 3.0% were cancelled.
What is the best time of day to fly BOS to SJU?
Flights scheduled to leave at 8 a.m. were the most reliable (77% on time). The 10 a.m. departures were the least (55%).
Which airline is most on time from BOS to SJU?
Delta Air Lines: 73% of its 398 flights on the route arrived on time. JetBlue: 65%. Spirit Airlines: 48%.
What month has the most delays from BOS to SJU?
February (56% on time). The best month is May (76%), over 2023–2026.
Is the last flight of the day from BOS to SJU more likely to be cancelled?
Not much. Each airline's last BOS–SJU flight of the day was cancelled 3.2% of the time over the past year, against 3.1% for its earlier flights. If the last flight is cancelled, the next one is usually the following morning.
Related
- SJU → BOS (return)
- Boston Logan (BOS) delays by hour
- Flights into San Juan (SJU)
- JetBlue on-time record
- Delta Air Lines on-time record
- Spirit Airlines on-time record
- Frontier Airlines on-time record
- Connecting off this flight? Check the risk
Domestic flights by the airlines that report to the U.S. DOT, plus their regional partners. "On time" means arriving less than 15 minutes after schedule; cancelled and diverted flights count as not on time. Past performance is a guide, not a forecast. Method.