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.
Processing and privacy
Processing varies by tool. Check the instructions for local processing, server requests, external services and any file or request limits before entering sensitive information.
Read the privacy policyHow this calculation works
Understand the method, inputs and limits behind your result.
- Formula
- Prevalence = existing cases / total population × selected multiplier. Confidence intervals use the exact binomial method.
- Variables
- Calculate from: Case counts, Incidence × duration
- Existing cases
- Population
- Incidence rate
- Average duration
- Express per: 100 people (percent), 1,000 people, 10,000 people, 100,000 people
- Confidence level: 90%, 95%, 99%
- Units
- Incidence rate: per 1,000/yr
- Average duration: years
- Example
- 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%).
- Assumptions
- 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.
- Source
- ToolzHive calculation guide and calculator implementation. External reference verification is pending.
- Last reviewed
- Review date not yet recorded.
Methodology & References
The method depends on the selected model and input options. Review the assumptions and references above before interpreting the result.
- Choose case counts, or incidence and duration.
- Enter the cases and population, or the incidence rate and average duration.
- Read the prevalence and its confidence interval.
Interpretation and limitations
- 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.
References
External reference verification is pending. The formula and examples describe the current ToolzHive implementation.
Share this tool
Found it useful? Send it to a friend or teammate.
Rate this tool
0.0
0 ratings
- 5 stars 0
- 4 stars 0
- 3 stars 0
- 2 stars 0
- 1 star 0
Clear instructions
Find steps, examples and limitations below.
Use online
Open the tool in a supported web browser.
Free to use
No sign-up required. Tool-specific limits may apply.
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.
Practical guides
-
How to Use Prevalence Calculator
Calculate point or period prevalence per 100, 1,000 or 100,000 with an exact confidence interval, or estimate prevalence from incidence and duration.
Report an issue
Something broken or not quite right? Tell us and we will look into it.