Carrier route record

NKBOS→SJU

Spirit Airlines · Boston to San Juan

Flights: 155
Period: July 2025 to June 2026
Share of route: 9%
Carriers: 4

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

Spirit on BOS to SJU earns an F−, which is as low as this site's scale goes for a reason. Only 54.5% of flights arrive inside the 15-minute window, 23 points worse than the national rate of 77.6%. Late arrivals average close to two hours. Treat any tight connection here as a coin flip. That rests on 155 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 398 at 76.0% on time.

The national on-time rate over the same period is 77.6%, so Spirit on BOS to SJU runs 23 points behind the country as a whole. Across a thousand flights that is about 231 extra late arrivals.

On time

54.5%

Arrivals under 15 minutes late, of 143 completed flights

Avg delay

105 min

Across delayed arrivals only, not all flights

Cancelled

7.74%

National rate is 1.81%

Whole route

69.0%

Every carrier on BOS to SJU, 1,819 flights

These figures cover 155 flights between July 2025 and June 2026. Beyond the headline rate, 20.3% 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 BOS to SJU

Spirit flew 155 of the 1,819 flights on BOS to SJU, about 9% of it. Its 54.5% on time is 15 points worse than the route as a whole, which runs 69.0%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from Delta at 76.0% to Frontier at 42.4%. 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 76.0% of the time; JetBlue Airways manages 69.2%. Sample sizes sit next to every figure, because a two-point gap across 1,232 flights means less than a ten-point one.

On-time performance by carrier on BOS to SJU
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	398	76.0%	57 min	1.51%	B
JetBlue Airways	1,232	69.2%	71 min	2.44%	C
Spirit Airlines (this page)thin sample	155	54.5%	105 min	7.74%	F−
Frontier Airlinesthin sample	34	42.4%	113 min	2.94%	F

Delta leads JetBlue by 7 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 is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 155 flights.

There are not enough flights in each departure window to split Spirit's BOS to SJU record by time of day without the percentages moving on noise. The headline rate of 54.5% is the reliable figure here.

Across the year

Spirit on BOS to SJU through the year

Jul–Sep 202512 flights—
Oct–Dec 202514 flights—
Jan–Mar 2026101 flights52.2%
Apr–Jun 202628 flights—

Scale runs 45% to 60%. 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 54.5% on time across 155 flights.

Split by quarter, Spirit on BOS to SJU logged 12 flights in Jul–Sep 2025, 14 flights in Oct–Dec 2025, 101 flights in Jan–Mar 2026 and 28 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 54.5% 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 48% of the 6,808 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
48%
Carrier
30%
Late-arriving aircraft
20%
Extreme weather
1%

48% 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 3,295 minutes out of 6,808, against a national NAS share of 21%. The split is drawn from 6,808 reported delay minutes.

Cancellations run at 7.74%, against 1.81% nationally. That is about one flight in twelve 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. 20.3% 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 72.8% on time across 154 flights, 18 points above 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. 155 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 BOS to SJU

Put together: the delay figures matter less here than the 7.74% cancellation rate. A late arrival costs you close to two hours; a cancelled flight costs you the day. Book the 2pm–5pm departure so there is still a schedule behind you if it goes wrong, and treat a same-day connection as optimistic. 143 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