Flight number record

UA 641

United Airlines · Washington to Boston

Route: IAD → BOS
Departs: 09:00
Flights: 344
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 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 14 points better than the national rate of 77.6%. When something does go wrong the average delay runs about an hour. That rests on 344 flights, with a median arrival 11 minutes early.

Set against the rest of the country, UA 641's record is 14 points better than the US average of 77.6%. That gap is worth roughly 138 fewer late arrivals for every thousand flights.

On time

91.4%

Arrivals under 15 minutes late, of 339 completed flights

Avg delay

55 min

Across delayed arrivals only, not all flights

Cancelled

1.45%

National rate is 1.81%

1 hour+ late

3.5%

National rate is 8.1%

These figures cover 344 flights between July 2025 and June 2026. The median arrival is 11 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.

Schedule

When UA 641 flies

UA 641 flies IAD to BOS without a single fixed slot. Its most common scheduled departure was 09:00, used on 111 of 344 flights, with 08:50 (80 flights) and 08:35 (62 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 09:00111 flights32.3%
Departs 08:5080 flights23.3%
Departs 08:3562 flights18.0%

Scale runs 0% to 100%. Rows with fewer than 30 flights show a dash.

Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.

A 09:00 departure sits in the 8am–11am window. Across every US flight scheduled in that window the on-time rate is 84.1%, and UA 641 runs 7 points better at 91.4%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.

Against the route

UA 641 next to IAD to BOS

Every carrier on IAD to BOS combined arrived on time 77.3% of the time across 1,462 flights, so UA 641 is 14 points ahead of it. United flew 1,459 flights on the same city pair under all its flight numbers, including this one, and those ran 77.4% on time. Across its whole network United Airlines managed 79.0%, which this flight beats by 12 points.

UA 641 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
UA 641thin sample	344	91.4%	55 min	1.45%	A
All United Airlines on IAD–BOS	1,459	77.4%	73 min	1.92%	B
All carriers on IAD–BOS	1,462	77.3%	73 min	1.92%	B
United Airlines, whole network	821,041	79.0%	72 min	1.01%	B

Across the year

UA 641 quarter by quarter

Quarter by quarter UA 641 held fairly steady: 89.1% in Jul–Sep 2025, 91.3% in Oct–Dec 2025, 93.8% in Jan–Mar 2026 and 92.2% in Apr–Jun 2026. A spread of 5 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.

Jul–Sep 202592 flights89.1%
Oct–Dec 202592 flights91.3%
Jan–Mar 202669 flights93.8%
Apr–Jun 202691 flights92.2%

Scale runs 80% to 100%. Rows with fewer than 30 flights show a dash.

By weekday, UA 641 ranged from 85.7% on Monday to 96.2% on Thursday. With about 49 flights behind each day, a spread of 11 points is inside normal variation, so the day you fly is not worth changing for this flight.

Delay causes

Why UA 641 runs late

One category carries most of the weight here. Late-arriving aircraft accounts for 47% of the 1,599 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.

Late-arriving aircraft
47%
National Airspace System
37%
Carrier
16%

47% 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 1,599 reported delay minutes here, that single category outweighs weather by 47 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 1,599 delay minutes reported on UA 641.

Cancellations sit at 1.45% against a national 1.81%, 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 3.5% land an hour or more behind schedule, against 8.1% 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 (73) 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: 91.4% on time and 1.45% cancelled. That is a base rate, not a promise about any single day.

Where to go next

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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures