Clinical Trial Recruitment Planner.
Work back from your target sample size to how many people to invite, screen and consent, and how long enrolment will take across your sites.
Enter your target, the funnel rates and your sites. The planner shows the people you need at each step, the expected finish month with a chance range, and a month by month plan you can download. Everything is calculated in your browser.
Month by Month Plan
Expected numbers screened and randomised each month at your planned rate, with the range of the running total of randomisations from chance alone.
Expected CONSORT enrolment numbers
How to Use the Recruitment Planner
- Enter your target. Choose completers if the number comes from a sample size calculation, or randomised if you already know how many people to randomise.
- Set the funnel. Enter dropout, screen failure and the consent rate. The fields start at published medians: replace them with figures from your area or your own pilot. Add a response rate if you invite people by letter, SMS, email or a registry.
- Choose the order of steps. Screen, then consent follows CONSORT, where eligibility is assessed before people decide to take part[1]. Consent, then screen suits protocols where trial screening procedures follow consent[2].
- Describe your sites. Enter the rate per open site per month, the number of sites and how they open.
- Read the plan. Add a start month for calendar dates, and download the month by month table as a CSV file.
For practical ways to fill each stage of the funnel, read our guides to clinical trial recruitment strategies and improving patient recruitment.
How the Planner Works Back From Your Target
The planner starts from the number you need at the end and divides by each conversion rate in turn, rounding up at every step. Every count multiplied by its rate then covers the next one, so you can check the funnel by hand.
Dropout: divide, do not multiply
Divide the completers you need by the share of randomised people you expect to keep:
Randomised = completers ÷ (1 − dropout), rounded up
For 400 completers and 12% dropout, that is 400 ÷ 0.88 = 454.5, so 455. A common shortcut multiplies by 1 + dropout instead: 400 × 1.12 = 448. After 12% dropout, 448 leaves about 394 completers, six short of the target. Multiplying always falls short, because for any dropout d, (1 + d) × (1 − d) = 1 − d², which is less than 1.
The funnel in CONSORT order
Eligible = randomised ÷ consent rate
Screened = eligible ÷ (1 − screen failure)
Invited = screened ÷ response rate
With the default medians, 455 randomised needs 632 eligible people and 973 screened. Here the consent rate is the share of eligible people who consent and are randomised, the definition behind the published median of 72%[3]. In the consent first order, screen failure is the share of consented people who fail screening and do not join the trial, the definition used in oncology reporting[4]. Both orders need the same number approached, apart from rounding. Only the middle steps change.
From Sites to Months
The rate is the number randomised per open site per month, the unit used by the large reviews of UK publicly funded trials[5][3]. Each site adds site months from the day it opens.
Expected randomised by month t = rate × site months open by month t
Finish month = first whole month in which the expected total reaches the target
With 17 sites open from month 1 at 0.86 per site per month, 455 randomisations need 455 ÷ 0.86 = 529 site months, or 31.1 months. The plan finishes in month 32.
Ramp up and custom schedules
With a ramp, sites open at an even pace. Once all sites are open, a ramp of T months finishes about T ÷ 2 months later than opening every site on day one, so a 6 month ramp moves the default plan from 31.1 to 34.1 months. In a custom schedule, sites added in a month open in the middle of that month.
Why 0.86 already includes ramp up
The published medians divide everyone recruited by the largest number of sites and the whole recruitment period. Both reviews note that this understates what an open site achieves, because sites open at different times[5][3]. Pairing 0.86 with all sites open reproduces the overall pace of those trials. With a ramp or a schedule, enter the rate of a site once it is open, which will be higher.
How to Read the Finish Month
A single date hides how uncertain recruitment is, so the planner adds two checks to the expected plan.
Expected finish
The month in which the expected running total reaches your target if every rate holds, such as month 32 for 31.1 months.
Chance range
People arrive at random even when the rates are right. Treating arrivals as a Poisson process, as published recruitment models do[6][7], the range shows where randomisation would finish in 8 out of 10 trials with exactly your rates.
Rate shortfall
The range covers chance only, not wrong assumptions. A rate set too high is the larger risk, so the planner also shows the finish at 75% and 50% of your rate. A third of UK publicly funded trials needed an extension[3].
Small targets
Chance matters most in small trials. With 10 participants at two sites recruiting 0.5 per site per month, the expected finish is month 10, but the chance range runs from month 7 to month 15.
Typical Rates in Published Trials
Treat these figures as a starting point. Rates vary widely by therapeutic area, setting and eligibility criteria, and most come from UK publicly funded trials, which may not match commercial trials[3].
| Measure | Published figure | Range and context |
|---|---|---|
| Participants per site per month | Median 0.86 in multicentre trials[5][3] | Middle half 0.40 to 2.17. General practice 0.71, hospitals 0.90, community settings 2.44[3] |
| Number of sites | Median 17[3] | Middle half 7 to 37 |
| Consent rate | Median 72% of eligible people consented and were randomised[3] | Middle half 50% to 88%. In US cancer studies, 55% of patients offered a trial agreed[8] |
| Screen failure | Median 65% of people screened were eligible, so 35% screen failure[9] | Middle half 41% to 82% eligible. Varies by area, see below |
| Dropout | Median 88% retained for the primary outcome, so 12% dropout[3] | Middle half 80% to 97% retained. 60.2% dropout in placebo arms of short antipsychotic trials[10] and 26.2% in trials of smartphone apps for depressive symptoms[11] |
Screen failure by therapeutic area
Definitions differ between studies, so compare like with like.
| Area | Published figure | How it was counted |
|---|---|---|
| Genitourinary cancers, phase II and III | Mean 19% to 26% across bladder, kidney and prostate trials[4] | Screened but did not join the trial |
| MASH trials with histology | 56% pooled across 58 trials[12] | Screened but did not join the trial |
| Resistant hypertension | 62% did not meet criteria for randomisation[13] | Two screening visits before randomisation |
| Preclinical Alzheimer’s disease | 70.5% did not have elevated amyloid[14] | One biomarker step only |
Use Your Own Feasibility Data
The most common reason given for recruitment failure is overestimating how many eligible people exist, and most of the reported reasons look preventable with a pilot that uses the planned consent procedure[15]. Optimism is built in too: a sizable minority of trial teams in the UK and Europe felt pressure to be optimistic about recruitment rates to make a trial attractive to funders[16].
A single external pilot is a weak guide to the main trial. Across 16 trials, pilot and main trial attrition differed by between −37.1 and +28.2 percentage points, and the share of eligible people randomised by between −47.8 and +77.5 points[17]. Internal pilots, built into the main trial and often judged against stop, amend or go criteria, are now common: 72.4% of 134 UK publicly funded trials from 2012 to 2016 planned one[18].
A completed screening log is an essential record under ICH E6(R3)[2], so your sites may already hold screening and consent rates from earlier or running studies to replace the medians.
Sites and Ramp Up
Sponsors and contract research organisations report that site start up takes 5 to 6 months on average, and repeat sites open faster than new ones[19]. Trials with fewer sites were more likely to finish without reaching their planned enrolment[20].
If you have a deadline, enter it to see how many sites the same opening pattern needs. With a 6 month ramp, finishing the default plan by month 24 needs 26 sites instead of 17.
Why Trials Fall Short
Recruitment problems are common and often start before anyone is approached.
Targets are often missed
Of 388 UK publicly funded trials, 63% reached their final target, but a third of those needed an extension, and only 53% reached the target they started with[3]. In an earlier cohort of 114 trials, 31% reached their original target[21].
Poor recruitment stops trials
Of 1,017 trials approved by ethics committees from 2000 to 2003, a quarter were discontinued, and poor recruitment was the most common reason[22]. A decade later, 30% of 326 trials were discontinued, most often for poor recruitment[23].
Fewer eligible people than expected
Among 2,579 phase 2 and 3 trials that closed in 2011, 19% stopped for poor accrual or finished below 85% of planned enrolment. More eligibility criteria were among the factors linked to failure[20].
Barriers before anyone decides
In US cancer care, no trial was available for 55.6% of patients and 21.5% were ineligible for the trial on offer. Only 8.1% joined a trial[24].
What Digital Screening, Consent and Retention Can Do
The evidence is narrower than marketing suggests. A systematic map of 105 comparative studies found most were observational and focused on recruitment rather than retention[25].
- eConsent. In 35 comparative studies with 13,281 participants, every study that compared comprehension found eConsent better or no different, and none favoured paper. Data on enrolment and retention were limited[26].
- Online recruitment. Online methods recruited faster per active day and cost less per participant recruited (US$72 against US$199), with no clear difference over the whole recruitment period. Offline recruits converted better[27]. If you recruit online, plan a lower conversion from screening to enrolment.
- Reminders and information. Telephone reminders to people who did not reply to a postal invitation raised recruitment by 6 percentage points. Adding a link or QR code to multimedia information alongside a paper leaflet made no difference to recruitment or retention[28].
- Retention. Electronic reminders and SMS or email prompts showed no clear effect on retention, while monetary incentives showed a benefit[29]. In smartphone mental health trials, online enrolment was linked to higher attrition[30].
WeGuide records each step of the funnel: eScreening with configurable eligibility checks, eConsent with versioned forms and an audit trail, and retention metrics that track dropout and inactive participants. An internal pilot then gives you your own screening, consent and dropout rates to enter here. See how this fits into WeGuide for clinical trials, and read our guide to patient retention in clinical trials.
Reporting Recruitment in a CONSORT Flow Diagram
CONSORT 2025 replaces CONSORT 2010 with a 30 item checklist and a flow diagram. It asks for the numbers randomly assigned, receiving the intended intervention and analysed for the primary outcome in each group, losses after randomisation with reasons, and the dates of recruitment and follow up[31]. The explanation and elaboration adds that the number of people assessed for eligibility, and the reasons for exclusion, should be reported if available[1].
Reporting is often incomplete. In 2004, 40% of trial reports in six major journals did not give the number assessed for eligibility[32], and in NIHR trials 68% reported every recruitment count from screened to analysed[3]. The planner’s expected CONSORT enrolment numbers use the same boxes, so you can compare your actual flow with the plan.
Limitations to Keep in Mind
- One rate for every site. Each open site recruits at the same average rate from opening until the target is met, with no warm up, closures or seasonal effects.
- Expected counts. Conversion rates stay constant over time and every count is an expected value. The chance range covers the timing of arrivals only, not variation in the funnel counts.
- No uncertainty about the rate itself. Models that add it, such as the Poisson gamma model, need an estimate of how sure you are of the rate[7]. Use the 75% and 50% rows instead.
- Benchmarks from one setting. The medians come mostly from UK publicly funded trials, which excluded cluster randomised trials[5][3].
- Planning only. This is not a sample size calculation and not medical advice.
Measure your own recruitment funnel
WeGuide’s eScreening, eConsent and retention metrics record each step of your funnel, so an internal pilot gives you your own screening, consent and dropout rates to plan the rest of your trial.
Frequently Asked Questions
Answers about recruitment rates, screen failure, dropout and planning enrolment time for a clinical trial.
Have another question?How many people do I need to screen to randomise my target?
Work backwards from the number to randomise, dividing by each conversion rate and rounding up. To randomise 455 people when 72% of eligible people consent, you need 632 eligible people. If 65% of the people you screen are eligible, you need to screen 973. These are median rates from UK publicly funded trials and from trials in major journals, so replace them with figures from your own area or a pilot where you can.
How do I adjust my sample size for dropout?
Divide the number of completers you need by the share you expect to keep. For 400 completers and 12% dropout, randomise 400 ÷ 0.88, which rounds up to 455. Do not multiply by 1.12, which gives 448 and leaves about 394 completers. The median UK publicly funded trial kept 88% of participants for its primary outcome, and the authors of that review suggest assuming at least 10% withdrawal when you have no better data.
What is a typical recruitment rate per site per month?
In multicentre trials funded by the UK NIHR, the median was 0.86 participants randomised per site per month, with the middle half of trials between 0.40 and 2.17. Rates were lower in general practice (0.71) than in hospitals (0.90) and community settings (2.44). These figures are averaged over the whole recruitment period, including months before sites opened, so an open site usually recruits faster than the published average.
How many trials reach their recruitment target?
Fewer than two thirds. Of 388 UK publicly funded trials, 63% reached their final target, but about a third of those needed an extension, and 30% had revised their original target, two thirds of them downwards. Only 53% reached the target they started with. An earlier review of 114 trials found that 31% reached their original target.
What screen failure rate should I expect?
It depends heavily on the condition and the eligibility criteria. A median of 65% of people screened were eligible in trials published in major journals. Genitourinary cancer trials reported mean screen failure of 19% to 26%, trials in MASH 56%, and a resistant hypertension trial 62%. A single biomarker test can exclude most people: 70.5% of those tested did not have elevated amyloid in the A4 study.
How does opening sites gradually change my timeline?
Each site recruits only from the day it opens, so a gradual opening pushes the finish back. Once all sites are open, a ramp of T months finishes about T ÷ 2 months later than opening every site on day one. Site start up takes 5 to 6 months on average, so plan the opening schedule as carefully as the recruitment rate, and enter the rate of a site once it is open.
Why does the planner show a range around the finish month?
Because people arrive at random, the finish month varies even when every rate is exactly right. The range shows where randomisation would finish in 8 out of 10 trials with your rates, from chance alone. It does not cover a rate that was set too high, which is the bigger risk, so the planner also shows the finish at 75% and 50% of your planned rate.
Can a pilot study tell me my recruitment and dropout rates?
It helps, but treat a single external pilot with caution. In 16 UK trials, attrition and the share of eligible people randomised often differed widely between the pilot and the main trial. Many UK trials now build an internal pilot into the main trial instead, judged against stop, amend or go criteria, and 72.4% of 134 trials funded from 2012 to 2016 planned one.
Do eConsent and digital recruitment speed up enrolment?
The evidence is mixed. eConsent improves understanding compared with paper, but data on its effect on enrolment and retention are limited. Online recruitment brings people in faster per day of active recruitment and costs less per participant recruited, but fewer of those people go on to enrol. Telephone reminders to people who do not reply to a postal invitation raise recruitment by about 6 percentage points.
What should my CONSORT flow diagram report about recruitment?
CONSORT 2025 asks for the number of participants randomised, receiving their intervention and analysed in each group, losses after randomisation with reasons, and the dates of recruitment. It also recommends reporting the number assessed for eligibility and the reasons for exclusion when available. The planner’s expected enrolment numbers follow the same structure, so you can compare your actual flow with the plan.
Related Research Tools
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References
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- International Council for Harmonisation. ICH E6(R3) Guideline for Good Clinical Practice. Final version adopted 6 January 2025. ICH E6(R3) PDF
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Method, defaults and figures checked against the original publications on 20 October 2026 by the WeGuide editorial team. Every PubMed ID was matched to its title in NCBI. This tool is for research planning and education. It is not a medical device and does not give medical advice.
