Carrier route record

NKSJU→BOS

Spirit Airlines · San Juan to Boston

Flights: 154
Period: July 2025 to June 2026
Share of route: 8%
Carriers: 4

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Spirit Airlines.

Spirit on SJU to BOS sits in the middle of the pack with a C−. About seven flights in ten arrive on time by the DOT's definition, 5 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 154 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 398 at 78.4% on time.

The national on-time rate over the same period is 77.6%, so Spirit on SJU to BOS runs 5 points behind the country as a whole. Across a thousand flights that is about 48 extra late arrivals.

On time

72.8%

Arrivals under 15 minutes late, of 147 completed flights

Avg delay

56 min

Across delayed arrivals only, not all flights

Cancelled

3.90%

National rate is 1.81%

Whole route

71.8%

Every carrier on SJU to BOS, 2,001 flights

These figures cover 154 flights between July 2025 and June 2026. Beyond the headline rate, 10.9% 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

Spirit against every carrier on SJU to BOS

Spirit flew 154 of the 2,001 flights on SJU to BOS, about 8% of it. Its 72.8% on time is about level with the route as a whole at 71.8%. Ranked by on-time rate it is number two of four carriers on the route, where the range runs from Delta at 78.4% to Frontier at 69.7%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 78.4% of the time; JetBlue Airways manages 69.9%. Sample sizes sit next to every figure, because a two-point gap across 1,415 flights means less than a ten-point one.

On-time performance by carrier on SJU to BOS
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	398	78.4%	70 min	1.51%	B
Spirit Airlines (this page)thin sample	154	72.8%	56 min	3.90%	C−
JetBlue Airways	1,415	69.9%	75 min	2.97%	C
Frontier Airlinesthin sample	34	69.7%	45 min	2.94%	C

Delta leads JetBlue by 9 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Departure window

When Spirit runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 28 points, against 9 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am—
8am–11am53 flights78.8%
11am–2pm53 flights82.4%
2pm–5pm48 flights54.5%
5pm–8pm—
8pm–5am—

Scale runs 45% to 90%. Rows with fewer than 30 flights show a dash.

The best window here is not the first bank but the 11am–2pm slot at 82.4% on time, ahead of 2pm–5pm at 54.5%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 8am–11am window is the busiest, with 53 flights scheduled in it.

Across the year

Spirit on SJU to BOS through the year

Jul–Sep 202512 flights—
Oct–Dec 202514 flights—
Jan–Mar 2026101 flights75.8%
Apr–Jun 202627 flights—

Scale runs 65% to 80%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 72.8% on time across 154 flights.

Split by quarter, Spirit on SJU to BOS logged 12 flights in Jul–Sep 2025, 14 flights in Oct–Dec 2025, 101 flights in Jan–Mar 2026 and 27 flights in Apr–Jun 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 72.8% annual figure is the one to use.

Delay causes

Why Spirit runs late on this route

One category carries most of the weight here. National Airspace System accounts for 47% of the 2,248 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.

National Airspace System
47%
Late-arriving aircraft
31%
Carrier
22%
Extreme weather
1%

47% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 1,047 minutes out of 2,248, against a national NAS share of 21%. The split is drawn from 2,248 reported delay minutes.

Cancellations run at 3.90%, against 1.81% nationally. That is about one flight in 25 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.

Connections and stage length

What a delay here costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 10.9% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

At 1,674 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 54.5% on time across 155 flights, 18 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 18 points of difference.

One caution: this is a thin sample. 154 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.

What to do with this

Booking Spirit on SJU to BOS

Put together: the delay figures matter less here than the 3.90% cancellation rate. A late arrival costs you about an hour; a cancelled flight costs you the day. Book the 11am–2pm departure so there is still a schedule behind you if it goes wrong, and treat a same-day connection as optimistic. 147 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures