Flight Reliability
UA 4521 · United Airlines
This number covered several routes in this period.
One number, several routes.
Airlines reuse flight numbers, and UA 4521 moved between routes during this period. Numbers below combine all of them, so treat them as background, not a verdict. For a cleaner answer, check the route you are actually flying.
Combined across all its routes
- 66%
- Arrive within 15 minutes
- 34 min
- Average arrival delay
- 6.3%
- Cancelled
- 1 min early
- Median arrival delay
Based on 334 historical flights. Data through May 2026.
The breakdown
- Mon57%(47 flights)
- Tue57%(44 flights)
- Wed68%(47 flights)
- Thu67%(49 flights)
- Fri71%(45 flights)
- Sat62%(37 flights)
- Sun79%(43 flights)
- 6–9 AM—(5 flights)
- 9 AM–12 PM84%(32 flights)
- 12–3 PM66%(130 flights)
- 3–6 PM66%(113 flights)
- 6–9 PM47%(32 flights)
87%
May
Jun 63% → May 87% on time
| Month | On-time percentage | Flights |
|---|---|---|
| June 2025 | 63% | 24 |
| July 2025 | 52% | 25 |
| August 2025 | 47% | 30 |
| September 2025 | 72% | 25 |
| October 2025 | 74% | 23 |
| November 2025 | 61% | 23 |
| December 2025 | 58% | 31 |
| January 2026 | 52% | 25 |
| February 2026 | 68% | 25 |
| March 2026 | 90% | 20 |
| April 2026 | 73% | 30 |
| May 2026 | 87% | 31 |
- Departures on time
- 70%
- Diverted
- 0.3%
- Flights flown
- 312
- Months covered
- 12
Keep nerding
Based on 334 historical flights, because apparently we checked. Historical flight data: U.S. Bureau of Transportation Statistics, June 2025 – May 2026. Data through May 2026. How we calculate this.