About 1 in 4 UA 721 flights from Boston arrived 15+ minutes late, diverted or cancelled over the past year (26%); 2.7% were cancelled. The typical flight landed 2 minutes early.
UA 721: BOS → IAD
Scheduled to leave Boston at 2:15 p.m. local time. Over the past year it arrived on time 74% of the time (365 flights), in line with other UA flights on the route at that hour (74%). Last seen in the data Aug 31, 2026.
Month by month
By day of week
| Day | Flights | On time |
|---|---|---|
| Monday | 53 | 77% |
| Tuesday | 52 | 81% |
| Wednesday | 52 | 65% |
| Thursday | 52 | 81% |
| Friday | 52 | 69% |
| Saturday | 52 | 79% |
| Sunday | 52 | 67% |
Why it was late
All flights BOS → IAD · Connecting off UA 721? Check the risk
Questions
How often is UA 721 from BOS to IAD late?
United Airlines 721 from Boston, MA to Washington, DC arrived 15 or more minutes late, was diverted or was cancelled on 26% of 365 scheduled flights between September 2025 and August 2026. 2.7% were cancelled.
Flight numbers change. Figures cover flights with this airline, number and route only. "Likely range" is the 95% interval for the true on-time rate given the number of flights. This is history, not live status: check United Airlines for today's flight. Method.