Trial Duration Estimator

Estimates the total duration of a clinical trial based on enrollment parameters, required sample size, follow-up period, and expected dropout rate.

Required Sample Size (participants)

Monthly Enrollment Rate (participants/month)

Expected Dropout Rate (%)

Follow-up Period per Participant (months)

Trial Startup Period (months)

Closeout Period (months)

Step 1 — Adjusted Sample Size:

n_adjusted = n / (1 − dropout_rate)

Step 2 — Enrollment Duration:

T_enrollment = n_adjusted / enrollment_rate

Step 3 — Total Trial Duration:

T_total = T_startup + T_enrollment + T_follow-up + T_closeout

Where all time units are in months.

Enrollment rate is assumed to be constant throughout the enrollment period.
Dropout is assumed to be uniformly distributed across participants; the sample size is inflated upfront to compensate.
Follow-up begins for each participant immediately after enrollment and is added as a single block after the last participant is enrolled (conservative estimate).
Startup covers site activation, IRB approval, and protocol finalization; closeout covers data lock and reporting.
Formula based on standard clinical trial planning methodology: Friedman, Furberg & DeMets — Fundamentals of Clinical Trials, 5th ed.
For multi-site trials, the effective enrollment rate should be the sum of all site-level rates.
This estimator does not account for interim analyses, adaptive designs, or seasonal enrollment variation.

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