Flight number record
UA 641
United Airlines · Washington to Boston
- Route
- IAD → BOS
- Departs
- 08:35
- Flights
- 344
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 641, check with United Airlines.
UA 641 earns an A. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 15 points better than the national rate of 77.3%. When something does go wrong the average delay runs roughly 55 minutes. That rests on 344 flights, with a median arrival 12 minutes early.
Set against the rest of the country, UA 641's record is 15 points better than the US average of 77.3%. That gap is worth roughly 150 fewer late arrivals for every thousand flights.
Key figures
On time
92.3%
Arrivals under 15 minutes late, of 339 completed flights
Avg delay
53 min
Across delayed arrivals only, not all flights
Cancelled
1.45%
National rate is 1.89%
1 hour+ late
3.2%
National rate is 8.3%
These figures cover 344 flights between September 2025 and August 2026. The median arrival is 12 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.
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Schedule
When UA 641 flies
UA 641 flies IAD to BOS without a single fixed slot. Its most common scheduled departure was 08:35, used on 124 of 344 flights, with 09:00 (111 flights) next.
- Departs 08:35124 flights36.0%
- Departs 09:00111 flights32.3%
Scale runs 0% to 100%.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 08:35 departure sits in the 8am–11am window. Across every US flight scheduled in that window the on-time rate is 83.9%, and UA 641 runs 8 points better at 92.3%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.
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Against the route
UA 641 next to IAD to BOS
Every carrier on IAD to BOS combined arrived on time 76.9% of the time across 1,524 flights, so UA 641 is 15 points ahead of it. United flew 1,447 flights on the same city pair under all its flight numbers, including this one, and those ran 77.1% on time. Across its whole network United Airlines managed 78.8%, which this flight beats by 14 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 641thin sample | 344 | 92.3% | 53 min | 1.45% | A |
| All United Airlines on IAD–BOS | 1,447 | 77.1% | 70 min | 2.07% | B |
| All carriers on IAD–BOS | 1,524 | 76.9% | 70 min | 2.76% | B |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 641 quarter by quarter
Quarter by quarter UA 641 held fairly steady: 93.3% in Jul–Sep 2025, 91.3% in Oct–Dec 2025, 93.8% in Jan–Mar 2026, 92.2% in Apr–Jun 2026 and 91.9% in Jul–Sep 2026. A spread of 3 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.
- Jul–Sep 202530 flights93.3%
- Oct–Dec 202592 flights91.3%
- Jan–Mar 202669 flights93.8%
- Apr–Jun 202691 flights92.2%
- Jul–Sep 202662 flights91.9%
Scale runs 85% to 100%.
By weekday, UA 641 ranged from 88.0% on Monday to 96.2% on Friday. With about 49 flights behind each day, a spread of 8 points is inside normal variation, so the day you fly is not worth changing for this flight.
Arrival by arrival
How late UA 641 runs when it is late
UA 641 often beats the schedule: 132 of 339 completed flights, 39%, arrived 15 minutes or more early. The 26 late arrivals split 12 under half an hour, 3 between 30 and 60 minutes, and 11 an hour or more.
- 15+ min early132 flights38.9%
- Within 15 min181 flights53.4%
- 15–29 min late12 flights3.5%
- 30–59 min late3 flights0.9%
- 1–2 hours late10 flights2.9%
- 2+ hours late1 flights0.3%
Scale runs 0% to 100%.
Share of 339 completed flights by arrival against schedule.
6 of 22 late departures made up the time and arrived on time, 27% of them. 10 flights left on time and still arrived late.
The worst days
Worst days for UA 641
The latest arrival of the period was on 27 October 2025, 2 hours 57 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The five worst days are spread across October, May, January and March, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 27 October 2025 | 2 hours 57 minutes | Late-arriving aircraft |
| 27 May 2026 | 1 hour 38 minutes | National Airspace System |
| 14 October 2025 | 1 hour 37 minutes | National Airspace System |
| 5 January 2026 | 1 hour 37 minutes | Late-arriving aircraft |
| 3 March 2026 | 1 hour 31 minutes | Carrier |
Delay causes
Why UA 641 runs late
National Airspace System accounts for 52% of the 1,371 delay minutes carriers reported here, and the remaining four split what is left.
- 52%National Airspace System
- 25%Late-arriving aircraft
- 23%Carrier
52% 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 719 minutes out of 1,371, against a national NAS share of 21%. The split is drawn from 1,371 delay minutes reported on UA 641.
Cancellations sit at 1.45% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
Badly late arrivals are rare here: only 3.2% land an hour or more behind schedule, against 8.3% 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.
The same number turns up on two other city pairs in the data, including ATL to IAD (114) and SNA to DEN (3), but none flew often enough under UA 641 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to IAD to BOS only.
One caution: this is a thin sample. 344 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking UA 641
For a booking, UA 641 has one of the better records a US domestic flight can show: 92.3% on time and 1.45% cancelled. That is a base rate, not a promise about any single day.
Related
Where to go next
- IAD to BOS, every carrier and departure
- BOS to IAD, the return direction
- United Airlines 688 on the same route61.4%
- United Airlines 755 on the same route79.1%
- Washington Dulles International (IAD) delay statistics
- Boston Logan International (BOS) delay statistics
- United Airlines on-time record
- Every United Airlines flight number with a record
- The most and least reliable flight numbers in the US
- Worst months to fly in the US, ranked by the data
A flight number here means United Airlines’s own number as it reports to the DOT. How the figures are computed is on the methodology page.
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.