Flight number record
UA 721
United Airlines · Boston to Washington
- Route
- BOS → IAD
- Departs
- 14:15
- Flights
- 365
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 721, check with United Airlines.
UA 721 lands a B, level with the national rate of 77.3%. About one flight in four arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That rests on 365 flights, with a median arrival 2 minutes early.
Key figures
On time
76.6%
Arrivals under 15 minutes late, of 354 completed flights
Avg delay
88 min
Across delayed arrivals only, not all flights
Cancelled
2.74%
National rate is 1.89%
1 hour+ late
9.3%
National rate is 8.3%
These figures cover 365 flights between September 2025 and August 2026. Beyond the headline rate, 9.3% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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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 141 of 365 flights, with 14:20 (53 flights) and 14:21 (37 flights) next.
- Departs 14:15141 flights38.6%
- Departs 14:2053 flights14.5%
- Departs 14:2137 flights10.1%
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 14:15 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 71.9%, and UA 721 runs 5 points better at 76.6%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.
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Against the route
UA 721 next to BOS to IAD
Every carrier on BOS to IAD combined arrived on time 83.2% of the time across 1,527 flights, so UA 721 is 7 points behind it. United flew 1,450 flights on the same city pair under all its flight numbers, including this one, and those ran 83.3% on time. Across its whole network United Airlines managed 78.8%, which this flight trails by 2 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 721 | 365 | 76.6% | 88 min | 2.74% | B |
| All United Airlines on BOS–IAD | 1,450 | 83.3% | 78 min | 2.28% | B |
| All carriers on BOS–IAD | 1,527 | 83.2% | 85 min | 3.01% | B− |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | 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 91 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 202530 flights—
- Oct–Dec 202592 flights67.8%
- Jan–Mar 202690 flights81.4%
- Apr–Jun 202691 flights84.4%
- Jul–Sep 202662 flights71.7%
Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.
By weekday, UA 721 did best on Tuesday at 84.0% on time and worst on Wednesday at 68.0%. Each day rests on about 52 flights, so a gap of 16 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 721 runs when it is late
The 83 late arrivals split 27 under half an hour, 23 between 30 and 60 minutes, and 33 an hour or more.
- 15+ min early45 flights12.7%
- Within 15 min226 flights63.8%
- 15–29 min late27 flights7.6%
- 30–59 min late23 flights6.5%
- 1–2 hours late16 flights4.5%
- 2+ hours late17 flights4.8%
Scale runs 0% to 100%.
Share of 354 completed flights by arrival against schedule.
Time lost at the gate mostly stays lost. Of 49 departures that left 15 minutes late or more, only 3 made it up before arrival. In the other direction, 37 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at IAD.
The worst days
Worst days for UA 721
The latest arrival of the period was on 28 July 2026, 19 hours 58 minutes behind schedule; most of its delay minutes were filed as national airspace system delay. The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 28 July 2026 | 19 hours 58 minutes | National Airspace System |
| 9 July 2026 | 6 hours 15 minutes | National Airspace System |
| 8 August 2026 | 6 hours 8 minutes | Extreme weather |
| 5 November 2025 | 6 hours 6 minutes | Late-arriving aircraft |
| 10 June 2026 | 4 hours 8 minutes | National Airspace System |
Delay causes
Why UA 721 runs late
National Airspace System accounts for 55% of the 7,295 delay minutes carriers reported here, and the remaining four split what is left.
- 55%National Airspace System
- 32%Late-arriving aircraft
- 8%Carrier
- 5%Extreme weather
55% 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 4,025 minutes out of 7,295, against a national NAS share of 21%. The split is drawn from 7,295 delay minutes reported on UA 721.
Cancellations run at 2.74%, 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 routes
What a delay on this flight costs
9.3% 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.
The same number turns up on one other city pair in the data, including IAD to LAS (18), 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. 365 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: 2.74% of its 365 scheduled flights did not operate. A late arrival costs an hour and a half, but a cancellation costs the day, so leave a later option open.
Related
Where to go next
- BOS to IAD, every carrier and departure
- IAD to BOS, the return direction
- United Airlines 2098 on the same route89.7%
- United Airlines 1734 on the same route96.1%
- United Airlines 2136 on the same route70.0%
- Boston Logan International (BOS) delay statistics
- Washington Dulles International (IAD) 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
- What a cancellation rate actually tells you (and what it hides)
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.