Clinical Trial Site Count
Estimate how many recruiting sites are required to meet a target enrollment within a fixed enrollment window after accounting for screen failures and startup lag.
Planning tool only. Confirm feasibility with site feasibility assessments, regulatory timelines, and trial operations leadership.
Examples
- 450 patients, 18-month window, 0.75 enrollments per site per month, 20% screen failure, 2-month startup ⇒ 47 sites required (46.88 exact).
- 200 patients, 12-month window, 0.90 enrollments per site per month, screen failure blank, startup blank ⇒ 19 sites required (18.52 exact).
FAQ
Why does the calculator round up the site count?
Site counts must be whole numbers. Rounding up ensures you have enough capacity to meet the enrollment target within the specified window.
What if some sites consistently outperform others?
Use a weighted average rate or model high-performing and low-performing cohorts separately. The calculator assumes a uniform average rate.
Should I include backup sites?
Yes, if backup sites are part of your operational plan. Add them by increasing the required site count or extending the enrollment window.
How should I treat protocol amendments?
If amendments pause enrollment, treat the pause as part of the startup delay or reduce the effective enrollment window accordingly.
Additional Information
- Result unit: number of active recruiting sites needed to hit the enrollment target.
- Screen failure defaults to 0% when blank; update it once early screening logs are available.
- Startup delay defaults to 0 months and should capture site activation and regulatory approval lead time.