Route reliability record
ISP→BWI
Islip to Baltimore
- Flights
- 1,217
- Period
- July 2025 to June 2026
- Distance
- 220 mi
- Carriers
- 1
This route earns a B. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.6%. When something does go wrong the average delay runs about an hour. That rests on 1,217 ISP to BWI flights, with a median arrival 7 minutes early.
Best time to fly ISP to BWI: a 5am–8am departure, ideally on a Friday. Flights in that window arrived on time 95.5% of the time and Friday flights 88.3%, against 84.9% for the route overall.
Set against the rest of the country, this route's record is 7 points better than the US average of 77.6%. That gap is worth roughly 73 fewer late arrivals for every thousand flights.
Key figures
On time
84.9%
Arrivals under 15 minutes late, of 1,195 completed flights
Avg delay
65 min
Across delayed arrivals only, not all flights
Cancelled
1.48%
National rate is 1.81%
Best carrier
Southwest
84.9% on time across 1,217 flights
These figures cover 1,217 flights between July 2025 and June 2026. The median arrival is 7 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 ISP to BWI
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Southwest Airlines | 1,217 | 84.9% | 65 min | 1.48% | B |
Best ways to make this trip
The most reliable ways to fly Islip to Baltimore
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 4 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. ISP → BWIIslip to Baltimore | Southwest Airlines | 83.6% | 84.9% | 1.48% | 5am–8am, Fri | — |
| 2. EWR → IADNewark to Washington | United Airlines | 72.2% | 73.9% | 2.24% | 5am–8am, Sat (route) | UA 1366 06:00 |
| 3. LGA → IADNew York to Washington | Republic Airways | 70.3% | 75.4% | 6.73% | 5am–8am, Sat | YX 3688 14:59 |
| 4. JFK → DCANew York to Washington | Republic Airways | 66.9% | 70.7% | 5.38% | 5am–8am, Sat | YX 4538 06:30 |
| 5. LGA → DCANew York to Washington | Republic Airways | 64.6% | 68.4% | 5.51% | 5am–8am, Sat (route) | YX 5770 06:00 |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 21 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am365 flights95.5%
- 8am–11am106 flights93.4%
- 11am–2pm328 flights82.8%
- 2pm–5pm267 flights75.2%
- 5pm–8pm151 flights75.0%
- 8pm–5am—
Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 95.5% of the time, against 75.0% for the evening window. That is 21 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 365 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 22 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.
July is the worst month at 74.0% on time, 22 points below September, the best at 95.6%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. June was the busiest month here, with 139 flights.
Across the week, Friday is the strongest day at 88.3% on time and Thursday the weakest at 82.3%. 6 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 45% of the 12,000 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.
- 45%Late-arriving aircraft
- 30%National Airspace System
- 24%Carrier
- 0%Extreme weather
45% 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 12,000 reported delay minutes here, that single category outweighs weather by 45 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 11,634 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 95.5% on time here.
Cancellations sit at 1.48% against a national 1.81%, which is ordinary. Diversions add another 0.33%.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.4% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
At 220 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 5am–8am window matters as much as it does.
The return leg is a different operation and performs like one: it runs 77.5% on time across 1,218 flights, 7 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 7 points of difference.
The sample behind these figures is 1,217 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.
Work out the risk of missing a connection in BWI after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 95.6% on time and July 74.0%, a swing of 22 points. If the dates move at all, move them out of July before you think about anything else. 1,195 completed flights over 12 months sit behind that.
Common questions
ISP to BWI questions
How often is ISP to BWI delayed?
About one flight in seven arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 15.1% of the 1,217 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is ISP to BWI compared with the rest of the country?
84.9% of flights arrive on time here against a national 77.6%, a difference of 7 points in its favour. That is worth a B on this site's grading scale.
What time of day has the fewest delays on ISP to BWI?
The 5am–8am departure window is the strongest at 95.5% on time. The 5pm–8pm window is the weakest at 75.0%, 21 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 July delays on ISP to BWI?
July is the weakest month at 74.0% on time, compared with 95.6% in September. Across the year that is 22 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- BWI to ISP — the return legseparate record
- Baltimore/Washington International Thurgood Marshall (BWI) delay statistics
- ISP to MCO, a related route72.8%
- ATL to BWI, a related route75.6%
- ISP to PBI, a related route71.9%
- Southwest Airlines on-time record84.9%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
Direction matters. ISP to BWI and BWI to ISP are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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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.