About 1 in 3 UA 521 flights from Houston arrived 15+ minutes late, diverted or cancelled over the past year (31%); 0.0% were cancelled. The typical flight landed 1 minutes late.
UA 521: IAH → BOS
Scheduled to leave Houston at 6:42 p.m. local time. Over the past year it arrived on time 69% of the time (153 flights), worse than other UA flights on the route at that hour (73%). Last seen in the data Aug 31, 2026.
Usually United Airlines's last flight of the day from Houston to Boston (100% of days). United Airlines's last IAH–BOS flight was cancelled 1.4% of the time, against 1.0% for its earlier ones. If it's cancelled, the next United Airlines flight is usually around 7:30 a.m. the next morning.
Month by month
By day of week
| Day | Flights | On time |
|---|---|---|
| Monday | 21 | 71% |
| Tuesday | 17 | — |
| Wednesday | 25 | 64% |
| Thursday | 26 | 69% |
| Friday | 25 | 72% |
| Saturday | 14 | — |
| Sunday | 25 | 60% |
Why it was late
All flights IAH → BOS · Connecting off UA 521? Check the risk
Questions
How often is UA 521 from IAH to BOS late?
United Airlines 521 from Houston, TX to Boston, MA arrived 15 or more minutes late, was diverted or was cancelled on 31% of 153 scheduled flights between September 2025 and August 2026. 0.0% 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.