Enrollment Projection Calculator

An enrollment projection calculator estimates how many patients a clinical trial can realistically enroll over a given period. It accounts for the catchment population, disease prevalence, eligibility criteria, screen failure rates, and dropout to give site teams and sponsors a data-driven forecast before the study starts.

The adjusted pool starts with the catchment population and applies disease prevalence to find the affected subgroup. That number is then reduced by the eligibility rate, screen failure rate, and competition from other studies to arrive at the realistic pool available for enrollment.

Screen failure rate is the percentage of patients who enter the screening process but do not qualify for enrollment — due to lab values, comorbidities, or other protocol criteria. A high screen failure rate (above 30%) significantly reduces the effective enrollment rate and can extend your study timeline.

When multiple trials target the same patient population in the same area, they compete for a finite pool of eligible patients. The calculator divides the eligible pool across all competing studies, reducing the share available to your trial. Reducing competition or expanding your catchment area can improve your projected enrollment.

Dropout rates vary by therapeutic area and study complexity. Phase II–III oncology studies may see 10–20% dropout, while long-duration chronic disease trials can exceed 25%. Most general clinical trials use a conservative estimate of 10–15%. Use historical data from similar studies at your site when available.

Success probability is a composite score based on how your projected enrollment compares to your target enrollment, adjusted for dropout and study duration. A high success probability (above 75%) means your current parameters are likely to meet the target on time; a low score signals the need to expand the site network, adjust eligibility, or increase budget.

If the projection falls short, consider expanding your catchment population by adding sites, broadening eligibility criteria to improve the eligibility rate, increasing the monthly budget to support more active outreach, or reducing screen failure through better pre-screening processes. Even modest improvements in each factor compound significantly.

Monthly budget drives the intensity of recruitment activities — advertising, site staff, patient outreach, and screening capacity. The calculator uses your budget alongside the patient pool to estimate a cost-per-patient figure, helping you assess whether your budget is sufficient to sustain the required monthly enrollment pace.