Route reliability record
BOS→IAD
Boston to Washington
- Flights
- 1,464
- Period
- July 2025 to June 2026
- Distance
- 412 mi
- Carriers
- 2
This route lands a B, 5 points better than the national rate of 77.6%. About one flight in six arrives 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 1,464 BOS to IAD flights, with a median arrival 8 minutes early.
Best time to fly BOS to IAD: a 11am–2pm departure, ideally on a Saturday. Flights in that window arrived on time 97.0% of the time and Saturday flights 87.3%, against 83.0% for the route overall.
Set against the rest of the country, this route's record is 5 points better than the US average of 77.6%. That gap is worth roughly 54 fewer late arrivals for every thousand flights.
Key figures
On time
83.0%
Arrivals under 15 minutes late, of 1,432 completed flights
Avg delay
76 min
Across delayed arrivals only, not all flights
Cancelled
2.05%
National rate is 1.81%
Best carrier
United
83.1% on time across 1,461 flights
These figures cover 1,464 flights between July 2025 and June 2026. The median arrival is 8 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 BOS to IAD
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 |
|---|---|---|---|---|---|
| United Airlines | 1,461 | 83.1% | 76 min | 2.05% | B |
| Republic Airwaysthin sample | 3 | 33.3% | 84 min | 0.00% | F+ |
Flight by flight
Flights on BOS to IAD
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
Best ways to make this trip
The most reliable ways to fly Boston to Washington
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. MHT → BWIManchester to Baltimore | Southwest Airlines | 87.0% | 87.7% | 0.75% | 5am–8am, Wed | — |
| 2. PVD → BWIProvidence to Baltimore | Southwest Airlines | 84.0% | 85.7% | 2.02% | 5am–8am, Wed | — |
| 3. BOS → IADBoston to Washington | United Airlines | 81.4% | 83.1% | 2.05% | 11am–2pm, Sat (route) | UA 1734 05:30 |
| 4. BOS → BWIBoston to Baltimore | Republic Airways | 79.2% | 81.9% | 3.31% | 5am–8am, Wed | YX 5644 17:25 |
| 5. PVD → DCAProvidence to Washington | Southwest Airlines | 76.8% | 78.9% | 2.68% | 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 28 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–8am346 flights96.8%
- 8am–11am365 flights91.1%
- 11am–2pm33 flights97.0%
- 2pm–5pm364 flights74.1%
- 5pm–8pm356 flights69.2%
- 8pm–5am—
Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 97.0% on time, ahead of 5pm–8pm at 69.2%. 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 8am–11am 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 17 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 71.9% on time, 17 points below May, the best at 89.3%. 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. September was the busiest month here, with 143 flights.
Across the week, Saturday is the strongest day at 87.3% on time and Thursday the weakest at 77.2%. 10 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 48% of the 18,000 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.
- 48%Late-arriving aircraft
- 32%National Airspace System
- 18%Carrier
- 2%Extreme weather
48% 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 18,000 reported delay minutes here, that single category outweighs weather by 24 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 18,428 reported delay minutes.
32% 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 5,912 minutes out of 18,000, against a national NAS share of 21%.
Cancellations sit at 2.05% against a national 1.81%, which is ordinary. Diversions add another 0.14%.
Connections and stage length
What a delay here actually costs
6.9% 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 a little over an hour, which a normal layover absorbs.
At 412 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 77.3% on time across 1,462 flights, 6 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 6 points of difference.
The sample behind these figures is 1,464 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 IAD 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. May runs 89.3% on time and July 71.9%, a swing of 17 points. If the dates move at all, move them out of July before you think about anything else. 1,432 completed flights over 12 months sit behind that.
Common questions
BOS to IAD questions
How often is BOS to IAD delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 17.0% of the 1,464 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.
How reliable is BOS to IAD compared with the rest of the country?
83.0% of flights arrive on time here against a national 77.6%, a difference of 5 points in its favour. That is worth a B on this site's grading scale.
What time of day has the fewest delays on BOS to IAD?
The 11am–2pm departure window is the strongest at 97.0% on time. The 5pm–8pm window is the weakest at 69.2%, 28 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 BOS to IAD?
July is the weakest month at 71.9% on time, compared with 89.3% in May. Across the year that is 17 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
- IAD to BOS — the return legseparate record
- Boston Logan International (BOS) delay statistics
- Washington Dulles International (IAD) delay statistics
- BOS to DCA, a related route74.0%
- ATL to IAD, a related route76.5%
- BOS to ORD, a related route72.7%
- United Airlines on-time record83.1%
- Republic Airways on-time record33.3%
- 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. BOS to IAD and IAD to BOS 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.