Enter start-up time, sites, activation, enrolment rate and follow-up. The calculator simulates enrolment week by week and shows when you reach first participant in, last participant in, database lock and topline results.
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Quarters
What drives trial timelines
Calculator
Sites are assumed to open evenly across the activation period, each enrolling at the rate you enter once open. Nothing you type is stored.
First participant in
Week 16
about 3.7 months
Last participant in
Week 79
about 18.2 months
Database lock
Week 111
about 25.5 months
Topline results
Week 117
about 26.9 months
Enrolment takes 63 weeks with sites opening evenly over the activation period. Defaults are placeholders, not benchmarks: use your own feasibility data.
Levers
Once you see the timeline, the question is where it can be shortened. The biggest gains usually come from the start-up phase and from enrolment, not from the treatment period, which the protocol fixes.
Contract and budget negotiation, ethics review and database build run partly in parallel. Building and testing the study while approvals are pending takes the database off the critical path; in Capture the AI Study Generator drafts the study from the protocol, and the free sandbox lets you test before anything is signed. See study start-up software.
More sites help only if they enrol; slow-activating sites add cost without speed. Pre-screening, QR enrolment and remote consent reduce the steps between a candidate and an enrolled participant. The sample size calculator and a realistic screen-failure rate tell you how many people you need to reach.
Studies that resolve queries as they arise and verify critical data continuously reach database lock in weeks rather than months after the last visit.
11
visits
9
draft forms
2
diaries
Build and test the study in the free sandbox while approvals run.
Worked example
With the defaults (16 weeks of start-up, 6 sites opening over 12 weeks, 1.5 participants per site per month, 120 participants, 24 weeks of treatment and follow-up, 8 weeks to lock and 6 weeks to topline), enrolment takes 63 weeks. The first participant enrols in week 16, the last in week 79, the last visit is in week 103, the database locks in week 111 and topline results arrive in week 117, about 27 months after the start.
Two quick experiments show the sensitivity. Increasing to 10 sites cuts enrolment from 63 to 40 weeks. Dropping the enrolment rate from 1.5 to 1.0 participants per site per month stretches it to 92 weeks, more than seven extra months. The enrolment rate is the input most worth checking against real data, for example from a pilot study or previous trials at the same sites.
Inputs
| Input | Best source | Common mistake |
|---|---|---|
| Start-up to first site open | Past studies with the same sites and approvals | Assuming contracts and approvals run faster than last time |
| Number of sites | Feasibility and site selection | Counting sites that will enrol little or nothing |
| Activation period | Site activation history | Assuming all sites open at once |
| Enrolment rate | Historical rates, pilot data | Using feasibility questionnaire estimates unadjusted |
| Treatment and follow-up | The protocol | Forgetting the safety follow-up after last dose |
| Lock and reporting | Data management plan | Planning lock without continuous cleaning |
Planning
A single timeline is a guess. Run the calculator three times, with optimistic, expected and pessimistic inputs for start-up and enrolment, and plan budgets and funding around the expected case with a clear view of the pessimistic one. Funders and boards react better to a range agreed in advance than to a delay announced later.
Once the study is running, compare actual enrolment by site with the plan every month. If enrolment falls behind, the options are the same levers the calculator shows: open more sites, extend the enrolment period, or review eligibility criteria through a protocol amendment if screen failures are the cause. The earlier the gap is seen, the cheaper each option is. A live enrolment dashboard makes that comparison routine; see clinical trial management software.
It depends on start-up, the number of sites, enrolment rates, treatment duration and close-out. The calculator estimates each phase from your inputs.
Sites open gradually and often enrol below feasibility estimates. Use historical rates where possible.
Week by week, with sites opening evenly over the activation period and each open site enrolling at the rate you enter.
No. They are placeholders to show how the calculation works.
No. The calculator runs in your browser.
Draft your study from the protocol in the free sandbox.