Route reliability record

SJU→ATL

San Juan to Atlanta

Flights: 2,126
Period: July 2025 to June 2026
Distance: 1,547 mi
Carriers: 3

This route lands a B, 4 points better than the national rate of 77.6%. About one flight in six arrive 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 2,126 flights, of which Delta Air Lines flew 1,637 at 90.8% on time.

Set against the rest of the country, this route's record is 4 points better than the US average of 77.6%. That gap is worth roughly 44 fewer late arrivals for every thousand flights.

On time

82.0%

Arrivals under 15 minutes late, of 2,084 completed flights

Avg delay

82 min

Across delayed arrivals only, not all flights

Cancelled

1.36%

National rate is 1.81%

Best carrier

Delta

90.8% on time across 1,637 flights

These figures cover 2,126 flights between July 2025 and June 2026. The median arrival is 10 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.

Carrier by carrier

Which airline is most reliable on SJU to ATL

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 90.8% of the time; Frontier Airlines manages 56.9%. Sample sizes sit next to every figure, because a two-point gap across 365 flights means less than a ten-point one.

On-time performance by carrier on SJU to ATL
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	1,637	90.8%	81 min	0.92%	A+
Frontier Airlines	365	56.9%	92 min	2.19%	D
Spirit Airlinesthin sample	124	37.3%	62 min	4.84%	F−

The spread between Delta and Frontier is 34 points, wide enough that it should decide the booking. On a hundred trips that is 34 more arrivals inside the on-time window.

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 14 points, against 34 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am614 flights91.2%
8am–11am6 flights—
11am–2pm298 flights78.1%
2pm–5pm761 flights76.9%
5pm–8pm443 flights80.8%
8pm–5am4 flights—

Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 91.2% of the time, against 76.9% for the afternoon window. That is 14 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 761 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 14 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.June best, March worst

Delays peak in March, when the on-time rate falls to 73.6%. June is the strongest month at 87.9%. Moving a flexible trip across that boundary buys 14 points. March was the busiest month here, with 229 flights.

Across the week, Wednesday is the strongest day at 88.5% on time and Sunday the weakest at 76.5%. 12 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

One category carries most of the weight here. Late-arriving aircraft accounts for 43% of the 31,000 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.

Late-arriving aircraft
43%
Carrier
37%
National Airspace System
19%
Extreme weather
1%
Security
0%

43% 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 31,000 reported delay minutes here, that single category outweighs weather by 43 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 30,603 reported delay minutes.

The largest share of delay minutes, 37%, 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 11,000 of the 31,000 delay minutes reported here.

Cancellations sit at 1.36% against a national 1.81%, which is ordinary. Diversions add another 0.61%.

Connections and stage length

What a delay here actually costs

6.3% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route are the a little over an hour kind, which a normal layover absorbs.

At 1,547 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 70.5% on time across 2,130 flights, 12 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 12 points of difference.

The sample behind these figures is 2,126 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. June runs 87.9% on time and March 73.6%, a swing of 14 points. If the dates move at all, move them out of March before you think about anything else. 2,084 completed flights over 12 months sit behind that.

Common questions

SJU to ATL questions

How often is SJU to ATL delayed?

About one flight in six arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 18.0% of the 2,126 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 SJU to ATL?

Delta Air Lines leads at 90.8% on time across 1,637 flights. Frontier Airlines is at the other end on 56.9%, a gap of 34 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 SJU to ATL?

The 5am–8am departure window is the strongest at 91.2% on time. The 2pm–5pm window is the weakest at 76.9%, 14 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 March delays on SJU to ATL?

March is the weakest month at 73.6% on time, compared with 87.9% in June. Across the year that is 14 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. SJU to ATL and ATL to SJU 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