Route reliability record
IAD→BOS
Washington to Boston
- Flights
- 1,462
- Period
- July 2025 to June 2026
- Distance
- 412 mi
- Carriers
- 2
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 a little over an hour on average. That is a workable record, not a spotless one. That rests on 1,462 IAD to BOS flights, with a median arrival 5 minutes early.
Best time to fly IAD to BOS: a 8am–11am departure, ideally on a Saturday. Flights in that window arrived on time 91.4% of the time and Saturday flights 85.3%, against 77.3% 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
77.3%
Arrivals under 15 minutes late, of 1,434 completed flights
Avg delay
73 min
Across delayed arrivals only, not all flights
Cancelled
1.92%
National rate is 1.81%
Best carrier
United
77.4% on time across 1,459 flights
These figures cover 1,462 flights between July 2025 and June 2026. Beyond the headline rate, 9.3% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
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 | 1,459 | 77.4% | 73 min | 1.92% | B |
| Republic Airwaysthin sample | 3 | 33.3% | 54 min | 0.00% | F+ |
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.
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 | 82.1% | 83.0% | 1.10% | 5am–8am, Tue | — |
| 2. BWI → BOSBaltimore to Boston | Republic Airways | 78.3% | 80.8% | 3.13% | 5am–8am, Sat | YX 5644 19:59 |
| 3. BWI → PVDBaltimore to Providence | Southwest Airlines | 77.8% | 79.3% | 1.92% | 5am–8am, Wed | — |
| 4. IAD → BOSWashington to Boston | United Airlines | 75.9% | 77.4% | 1.92% | 8am–11am, Sat (route) | UA 641 09:00 |
| 5. DCA → PVDWashington to Providence | American Airlines | 75.2% | 76.7% | 1.99% | 2pm–5pm, 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 62 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–8am—
- 8am–11am344 flights91.4%
- 11am–2pm365 flights80.9%
- 2pm–5pm32 flights29.0%
- 5pm–8pm365 flights60.2%
- 8pm–5am356 flights81.3%
Scale runs 20% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 91.4% of the time, against 29.0% for the afternoon window. That is 62 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm 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 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. September was the busiest month here, with 142 flights.
Across the week, Saturday is the strongest day at 85.3% on time and Monday the weakest at 72.5%. 13 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. National Airspace System accounts for 56% of the 24,000 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.
- 56%National Airspace System
- 20%Late-arriving aircraft
- 18%Carrier
- 6%Extreme weather
56% 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 13,000 minutes out of 24,000, against a national NAS share of 21%. The split is drawn from 23,833 reported delay minutes.
Cancellations sit at 1.92% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here actually costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.3% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum 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 83.0% on time across 1,464 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 1,462 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. 1,434 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 22.7% of the 1,462 flights in this analysis, against 22.4% 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?
77.3% 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 IAD to BOS?
The 8am–11am departure window is the strongest at 91.4% on time. The 2pm–5pm window is the weakest at 29.0%, 62 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 route79.2%
- DCA to BOS, a related route71.4%
- IAD to DEN, a related route81.7%
- United Airlines on-time record77.4%
- Republic Airways on-time record33.3%
- How often a connection fails at the major US hubs
- The best time of day to fly, according to 7.04 million flight records
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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.