Last updated October 13, 2026 · Report an error
Computes the standard published epidemiology incidence rate: Incidence Rate = new cases / (population at risk x time period), expressed per a chosen multiplier (e.g. per 1,000 or per 100,000 person-years). This is the standard person-time incidence rate formula taught in public health and epidemiology statistics. Pure arithmetic given the inputs. For general reference and educational purposes only.
How it works
Enter the number of new cases, the population at risk, the time period in years, and a multiplier. The tool divides new cases by (population x time) and multiplies by the chosen multiplier.
- Enter new cases during period.
- Enter population at risk.
- Enter time period (years).
- Enter express per.
- Click Calculate to see your results.
Examples
10 new cases, population 1,000, 1 year, per 1,000
Incidence rate = (10 / (1000 x 1)) x 1000 = 10 per 1,000 person-years.
Who should use it
- Public health statistics education.
- Reviewing epidemiology study reports.
Industry applications
- Public health reporting
- Epidemiology education
Advantages
- Standard, widely-taught public health formula.
- Flexible multiplier for readability.
Limitations
- Assumes a stable population at risk over the time period.
- Does not account for varying individual follow-up times.
Common mistakes to avoid
- Confusing incidence rate (per person-time) with cumulative incidence (simple proportion over a fixed period).
Best practices
- Make sure the population-at-risk figure excludes people who cannot develop the outcome (e.g. those already immune or already affected), per standard epidemiology practice.
Tips
- Person-time incidence rates are most meaningful when the population at risk is relatively stable over the study period.