Flight number record

UA 721

United Airlines · Boston to Washington

Route: BOS → IAD
Departs: 14:15
Flights: 316
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s UA 721, check with United Airlines.

UA 721 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 316 flights, with a median arrival 2 minutes early.

On time

77.5%

Arrivals under 15 minutes late, of 307 completed flights

Avg delay

69 min

Across delayed arrivals only, not all flights

Cancelled

2.53%

National rate is 1.81%

1 hour+ late

8.8%

National rate is 8.1%

These figures cover 316 flights between July 2025 and June 2026. Beyond the headline rate, 8.8% 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.

Schedule

When UA 721 flies

UA 721 flies BOS to IAD without a single fixed slot. Its most common scheduled departure was 14:15, used on 100 of 316 flights, with 14:20 (53 flights) and 14:21 (37 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 14:15100 flights31.6%
Departs 14:2053 flights16.8%
Departs 14:2137 flights11.7%

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 14:15 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 72.4%, and UA 721 runs 5 points better at 77.5%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.

Against the route

UA 721 next to BOS to IAD

Every carrier on BOS to IAD combined arrived on time 83.0% of the time across 1,464 flights, so UA 721 is 6 points behind it. United flew 1,461 flights on the same city pair under all its flight numbers, including this one, and those ran 83.1% on time. Across its whole network United Airlines managed 79.0%, which this flight trails by 2 points.

UA 721 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
UA 721thin sample	316	77.5%	69 min	2.53%	B
All United Airlines on BOS–IAD	1,461	83.1%	76 min	2.05%	B
All carriers on BOS–IAD	1,464	83.0%	76 min	2.05%	B
United Airlines, whole network	821,041	79.0%	72 min	1.01%	B

Across the year

UA 721 quarter by quarter

UA 721 did not run the same all year. Its best quarter was Apr–Jun 2026 at 84.4% on time and its weakest Oct–Dec 2025 at 67.8%, a swing of 17 points on roughly 79 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.

Jul–Sep 202543 flights75.6%
Oct–Dec 202592 flights67.8%
Jan–Mar 202690 flights81.4%
Apr–Jun 202691 flights84.4%

Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.

By weekday, UA 721 did best on Tuesday at 84.4% on time and worst on Sunday at 69.8%. Each day rests on about 45 flights, so a gap of 15 points is worth noticing but could still narrow in another year.

Delay causes

Why UA 721 runs late

One category carries most of the weight here. Late-arriving aircraft accounts for 46% of the 4,728 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
46%
National Airspace System
44%
Carrier
10%
Extreme weather
0%

46% 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 4,728 reported delay minutes here, that single category outweighs weather by 46 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 4,728 delay minutes reported on UA 721.

Cancellations run at 2.53%, against 1.81% nationally. That is about 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 routes

What a delay on this flight costs

8.8% 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.

The same number turns up on four other city pairs in the data, including ORD to BOS (42), IAD to LAS (18) and IAH to SAT (4), but none flew often enough under UA 721 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to BOS to IAD only.

One caution: this is a thin sample. 316 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 721

For a booking, the cancellation rate is the figure to plan around on UA 721: 2.53% of its 316 scheduled flights did not operate. A late arrival costs a little over an hour, but a cancellation costs the day, so leave a later option open.

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