Route reliability record
BWI→ISP
Baltimore to Islip
- Flights
- 1,218
- Period
- July 2025 to June 2026
- Distance
- 220 mi
- Carriers
- 1
This route lands a B, level with the national rate of 77.6%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by about 45 minutes on average. That is a workable record, not a spotless one. That rests on 1,218 BWI to ISP flights, with a median arrival 2 minutes early.
Best time to fly BWI to ISP: a 11am–2pm departure, ideally on a Friday. Flights in that window arrived on time 87.2% of the time and Friday flights 82.0%, against 77.5% for the route overall.
The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
77.5%
Arrivals under 15 minutes late, of 1,189 completed flights
Avg delay
46 min
Across delayed arrivals only, not all flights
Cancelled
1.97%
National rate is 1.81%
Best carrier
Southwest
77.5% on time across 1,218 flights
These figures cover 1,218 flights between July 2025 and June 2026. The median arrival is 2 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 BWI to ISP
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 | 1,218 | 77.5% | 46 min | 1.97% | B |
Best ways to make this trip
The most reliable ways to fly Baltimore to Islip
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. DCA → JFKWashington to New York | JetBlue Airways | 77.1% | 81.9% | 5.83% | 5am–8am, Wed | — |
| 2. BWI → ISPBaltimore to Islip | Southwest Airlines | 76.0% | 77.5% | 1.97% | 11am–2pm, Fri | — |
| 3. IAD → EWRWashington to Newark | United Airlines | 73.5% | 75.2% | 2.23% | 5am–8am, Wed (route) | UA 2669 06:00 |
| 4. DCA → JFKWashington to New York | Republic Airways | 73.1% | 77.2% | 5.37% | 5am–8am, Sat | YX 5713 17:00 |
| 5. IAD → LGAWashington to New York | Republic Airways | 69.0% | 73.8% | 6.53% | 8am–11am, Sat | — |
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–8am18 flights—
- 8am–11am292 flights85.7%
- 11am–2pm165 flights87.2%
- 2pm–5pm305 flights79.0%
- 5pm–8pm74 flights66.7%
- 8pm–5am364 flights66.3%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 87.2% on time, ahead of 8pm–5am at 66.3%. 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 8pm–5am window is the busiest, with 364 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 25 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 63.9% on time, 25 points below January, the best at 88.9%. 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 138 flights.
Across the week, Friday is the strongest day at 82.0% on time and Sunday the weakest at 65.8%. 16 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 50% 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.
- 50%Late-arriving aircraft
- 42%Carrier
- 5%National Airspace System
- 3%Extreme weather
- 0%Security
50% 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 16 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 12,330 reported delay minutes.
The largest share of delay minutes, 42%, 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 5,129 of the 12,000 delay minutes reported here.
Cancellations sit at 1.97% against a national 1.81%, which is ordinary. Diversions add another 0.41%.
Connections and stage length
What a delay here actually costs
5.3% 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 last about 45 minutes, which a normal layover absorbs.
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 11am–2pm window matters as much as it does.
The return leg is a different operation and performs like one: it runs 84.9% on time across 1,217 flights, 7 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 7 points of difference.
The sample behind these figures is 1,218 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 ISP 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. January runs 88.9% on time and July 63.9%, a swing of 25 points. If the dates move at all, move them out of July before you think about anything else. 1,189 completed flights over 12 months sit behind that.
Common questions
BWI to ISP questions
How often is BWI to ISP delayed?
Roughly one flight in four arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.5% of the 1,218 flights in this analysis, against 22.4% nationally. Delayed flights are late by about 45 minutes on average.
How reliable is BWI to ISP compared with the rest of the country?
77.5% of flights arrive on time here against a national 77.6%, a difference of half a point against it. That is worth a B on this site's grading scale.
What time of day has the fewest delays on BWI to ISP?
The 11am–2pm departure window is the strongest at 87.2% on time. The 8pm–5am window is the weakest at 66.3%, 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 BWI to ISP?
July is the weakest month at 63.9% on time, compared with 88.9% in January. Across the year that is 25 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
- ISP to BWI — the return legseparate record
- Baltimore/Washington International Thurgood Marshall (BWI) delay statistics
- BWI to ATL, a related route80.6%
- MCO to ISP, a related route74.8%
- BWI to MCO, a related route75.6%
- Southwest Airlines on-time record77.5%
- 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. BWI to ISP and ISP to BWI are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Embed BWI to ISP’s on-time badge on your site
Paste this into a web page. The badge shows the current on-time rate, cancellation rate and grade, and updates every month. Preview it, or build a badge for another route or airport.
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.