Boston (BOS) to San Juan (SJU): On-Time Performance
Data through July 2026
When you fly BOS to SJU matters as much as anything else about the booking: the route swung from 84% on-time in September 2024 to just 54% in December 2024. Across the full period the route averages 67% on-time against a national 78%. Morning departures also hold up better than evening ones (74% vs 57%), which matters most in the rough months.
- On-time
- 67%
- arrived <15 min late
- Avg delay
- 26 min
- completed flights
- Cancelled
- 1.9%
- Flights/day
- 4.8
- last 12 months
- Duration
- 4h 3m
- scheduled
- Distance
- 1,674 mi
Best airline from BOS to SJU
4 airlines flew this route regularly between 2024-07 and 2026-07.
| Airline | On-time | Avg delay | Cancelled | Flights |
|---|---|---|---|---|
| Delta Air Linesmost reliable | 78% | 14 min | 1.0% | 828 |
| JetBlue Airways | 68% | 25 min | 1.6% | 2,704 |
| Spirit Airlines | 54% | 42 min | 6.2% | 289 |
| Frontier Airlines | 42% | 64 min | 3.1% | 227 |
Monthly on-time trend
Best time to fly from BOS to SJU
Aim for departures around 8 a.m. (81% on-time); avoid 9 p.m. departures (33%).
By day of week
| Day | On-time | Avg delay |
|---|---|---|
| Monday | 65% | 31 min |
| Tuesdaybest | 72% | 22 min |
| Wednesday | 71% | 22 min |
| Thursday | 63% | 26 min |
| Friday | 69% | 24 min |
| Saturday | 69% | 22 min |
| Sunday | 65% | 32 min |
What causes delays on this route
Share of total delay minutes by cause, as reported by carriers to the US DOT.
- Late-arriving aircraft31%
- Airline operations37%
- National airspace system29%
- Weather3%
Frequently asked questions
- How often are flights from BOS to SJU delayed?
- 33% of BOS–SJU flights arrived 15 or more minutes late (the US DOT definition of a delay) between 2024-07 and 2026-07. The average arrival delay across completed flights was 26 minutes.
- Which airline is most reliable from BOS to SJU?
- Delta Air Lines has the best on-time record on this route at 78%, based on 828 flights. 4 airlines flew BOS–SJU frequently enough to compare in this period.
- What is the best time of day to fly from BOS to SJU?
- Departures around 8 a.m. have the best record (81% on-time), while departures around 9 p.m. have the worst (33%). As on most US routes, delays accumulate through the day, so earlier flights are generally safer.
- How long is the flight from BOS to SJU?
- The scheduled BOS–SJU flight time averages 4h 3m over 1,674 miles. Actual arrival times vary — flights on this route land 15+ minutes late 33% of the time.
- How often are BOS to SJU flights cancelled?
- 1.9% of scheduled flights on this route were cancelled between 2024-07 and 2026-07, slightly above the national rate of 1.6%.
- What is the worst month to fly from BOS to SJU?
- December 2024 was the roughest month in this dataset, with only 54% of arrivals on time. The best was September 2024 at 84%. If your dates are flexible, that 30-point gap is worth planning around.
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Based on 4,048 flights, 2024-07–2026-07. Source: US DOT Bureau of Transportation Statistics. Updated 2026-09-28.