Route reliability record

JFK→SJU

New York to San Juan

Flights: 3,651
Period: July 2025 to June 2026
Distance: 1,598 mi
Carriers: 3

This route sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 7 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 3,651 flights, of which Delta Air Lines flew 1,104 at 78.8% on time.

The national on-time rate over the same period is 77.6%, so this route runs 7 points behind the country as a whole. Across a thousand flights that is about 65 extra late arrivals.

On time

71.1%

Arrivals under 15 minutes late, of 3,549 completed flights

Avg delay

74 min

Across delayed arrivals only, not all flights

Cancelled

2.63%

National rate is 1.81%

Best carrier

Delta

78.8% on time across 1,104 flights

These figures cover 3,651 flights between July 2025 and June 2026. Beyond the headline rate, 11.0% 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

Which airline is most reliable on JFK to SJU

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 78.8% of the time; JetBlue Airways manages 69.5%. Sample sizes sit next to every figure, because a two-point gap across 2,232 flights means less than a ten-point one.

On-time performance by carrier on JFK to SJU
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	1,104	78.8%	60 min	1.99%	B
JetBlue Airways	2,232	69.5%	74 min	2.91%	C
Frontier Airlinesthin sample	315	56.1%	99 min	2.86%	D

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

Departure window

The best time of day to leave

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 13 points, against 9 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am456 flights77.6%
8am–11am767 flights77.0%
11am–2pm914 flights72.5%
2pm–5pm270 flights67.9%
5pm–8pm709 flights64.8%
8pm–5am535 flights64.9%

Scale runs 55% to 85%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 64.8% on time, against 77.6% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 11am–2pm window is the busiest, with 914 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 20 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.

Darker means more delays. Figures are on-time percentages.May best, October worst

May is the best month on the calendar at 82.2% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. July was the busiest month here, with 371 flights.

Across the week, Tuesday is the strongest day at 75.9% on time and Thursday the weakest at 64.0%. 12 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 76,000 reported delay minutes.

Carrier
38%
Late-arriving aircraft
35%
National Airspace System
25%
Extreme weather
2%
Security
1%

35% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 76,000 reported delay minutes here, that single category outweighs weather by 20 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 75,651 reported delay minutes.

The largest share of delay minutes, 38%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 28,000 of the 76,000 delay minutes reported here.

Cancellations run at 2.63%, against 1.81% nationally. That is about one flight in 40 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 actually costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 11.0% 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 1,598 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 79.3% on time across 3,657 flights, 8 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 8 points of difference.

The sample behind these figures is 3,651 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.

What to do with this

Booking this route

Put together: the calendar is the biggest lever here, not the carrier or the hour. May runs 82.2% on time and October 62.7%, a swing of 20 points. If the dates move at all, move them out of October before you think about anything else. 3,549 completed flights over 12 months sit behind that.

Common questions

JFK to SJU questions

How often is JFK to SJU delayed?

Roughly one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 28.9% of the 3,651 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on JFK to SJU?

Delta Air Lines leads at 78.8% on time across 1,104 flights. JetBlue Airways is at the other end on 69.5%, a gap of 9 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.

What time of day has the fewest delays on JFK to SJU?

The 5am–8am departure window is the strongest at 77.6% on time. The 5pm–8pm window is the weakest at 64.8%, 13 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.

How bad are October delays on JFK to SJU?

October is the weakest month at 62.7% on time, compared with 82.2% in May. Across the year that is 20 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. JFK to SJU and SJU to JFK are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures