Route reliability record
IAD→BOS
Washington to Boston
- Flights
- 1,524
- Period
- September 2025 to August 2026
- Distance
- 412 mi
- Carriers
- 2
This route lands a B, level with the national rate of 77.3%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That rests on 1,524 IAD to BOS flights, with a median arrival 6 minutes early.
Best time to fly IAD to BOS: a 8am–11am departure, ideally on a Saturday. Flights in that window arrived on time 91.5% of the time and Saturday flights 84.6%, against 76.9% for the route overall.
The US average over the same twelve months is 77.3%, 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
76.9%
Arrivals under 15 minutes late, of 1,482 completed flights
Avg delay
70 min
Across delayed arrivals only, not all flights
Cancelled
2.76%
National rate is 1.89%
Best carrier
United
77.1% on time across 1,447 flights
These figures cover 1,524 flights between September 2025 and August 2026. Beyond the headline rate, 9.2% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Which airline is most reliable on IAD to BOS
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 | 1,447 | 77.1% | 70 min | 2.07% | B |
| Republic Airwaysthin sample | 77 | 72.3% | 76 min | 15.58% | C− |
Flight by flight
Flights on IAD to BOS
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.
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Best ways to make this trip
The most reliable ways to fly Washington to Boston
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. BWI → MHTBaltimore to Manchester | Southwest Airlines | 83.0% | 84.2% | 1.39% | 5am–8am, Wed | — |
| 2. BWI → PVDBaltimore to Providence | Southwest Airlines | 77.8% | 79.6% | 2.28% | 5am–8am, Wed | — |
| 3. BWI → BOSBaltimore to Boston | Republic Airways | 77.2% | 80.5% | 4.09% | 5am–8am, Sat | YX 5703 10:54 |
| 4. IAD → BOSWashington to Boston | United Airlines | 75.5% | 77.1% | 2.07% | 8am–11am, Sat (route) | UA 641 08:35 |
| 5. DCA → PVDWashington to Providence | American Airlines | 74.4% | 77.0% | 3.33% | 8am–11am, Tue | — |
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 53 points, against half a point between the best and worst carrier.
- 5am–8am—
- 8am–11am381 flights91.5%
- 11am–2pm365 flights79.4%
- 2pm–5pm59 flights38.3%
- 5pm–8pm365 flights61.2%
- 8pm–5am354 flights79.5%
Scale runs 30% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 91.5% of the time, against 38.3% for the afternoon window. That is 53 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 381 flights scheduled in it.
Explore
Filter IAD to BOS by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On IAD to BOS, the best departure window is 8am–11am at 91.5% on time and the worst is 2pm–5pm at 38.3%, a wide gap of 53.2 points. All US flights leaving 8am–11am ran 83.9%.
- 5–8am—
- 8–11am91.5%
- 11am–2pm79.4%
- 2–5pm38.3%
- 5–8pm61.2%
- 8pm–5am79.5%
best all US flightsScale 30% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 30 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.
Delays peak in September, when the on-time rate falls to 57.9%. January is the strongest month at 87.5%. Moving a flexible trip across that boundary buys 30 points. July was the busiest month here, with 176 flights.
Across the week, Saturday is the strongest day at 84.6% on time and Monday the weakest at 70.4%, a spread of 14 points.
Delay causes
Why this route gets delayed
National Airspace System accounts for 63% of the 24,000 delay minutes carriers reported here, and the remaining four split what is left.
- 63%National Airspace System
- 18%Late-arriving aircraft
- 15%Carrier
- 4%Extreme weather
63% 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 15,000 minutes out of 24,000, against a national NAS share of 21%. The split is drawn from 24,063 reported delay minutes.
Cancellations run at 2.76%, against 1.89% nationally. That is roughly 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
9.2% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection here, and two hours if the onward flight is on a separate ticket.
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 8am–11am window matters as much as it does.
The return leg is a different operation and performs like one: it runs 83.2% on time across 1,527 flights, 6 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 6 points of difference.
The sample behind these figures is 1,524 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 BOS 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 87.5% on time and September 57.9%, a swing of 30 points. If the dates move at all, move them out of September before you think about anything else. 1,482 completed flights over 12 months sit behind that.
Common questions
IAD to BOS questions
How often is IAD to BOS 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 23.1% of the 1,524 flights in this analysis, against 22.7% nationally. Delayed flights are late by a little over an hour on average.
How reliable is IAD to BOS compared with the rest of the country?
76.9% of flights arrive on time here against a national 77.3%, 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 IAD to BOS?
The 8am–11am departure window is the strongest at 91.5% on time. The 2pm–5pm window is the weakest at 38.3%, 53 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 September delays on IAD to BOS?
September is the weakest month at 57.9% on time, compared with 87.5% in January. Across the year that is 30 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
- BOS to IAD — the return legseparate record
- Washington Dulles International (IAD) delay statistics
- Boston Logan International (BOS) delay statistics
- IAD to ATL, a related route78.0%
- DCA to BOS, a related route70.1%
- IAD to DEN, a related route83.1%
- United Airlines on-time record77.1%
- Republic Airways on-time record72.3%
- The US routes with the most cancellations
- What a cancellation rate actually tells you (and what it hides)
Direction matters. IAD to BOS and BOS to IAD 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.