Prevalence Calculator
Point or period prevalence with confidence interval, or from incidence and duration.
Enter your values to see the result.
The incidence × duration method assumes a steady state: P = ID ÷ (1 + ID). Confidence intervals use exact (Clopper–Pearson or Poisson) methods. Rates are only comparable between populations with similar age structures unless you standardize them.
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- Sample Size Calculator — Plan a prevalence survey.
- Incidence Calculator — Calculate new-case risk.
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Clear instructions
Find steps, examples and limitations below.
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How to use the Prevalence Calculator
Point or period prevalence with confidence interval, or from incidence and duration.
- 1 Choose case counts, or incidence and duration.
- 2 Enter the cases and population, or the incidence rate and average duration.
- 3 Read the prevalence and its confidence interval.
Example and practical tips
180 cases in a population of 2,400 is a prevalence of 75 per 1,000 (7.5%, 95% CI 6.48% to 8.63%).
Frequently asked questions
How does duration affect prevalence?
In a steady state prevalence ≈ incidence × duration, so long-lasting conditions are more prevalent even at the same incidence.
Point or period prevalence?
Point prevalence counts cases on one date; period prevalence counts anyone affected during a period, such as a year.
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