Risk Calculator
Enter the number of events, population at risk, and optional time horizon to compute risk (incidence proportion), incidence rate, and odds.
Number of observed events (cases).
Total number of individuals observed.
Person-time units (e.g., years). Leave as 1 if not applicable.
Risk (Incidence Proportion)
6.25%
Events / Population
Incidence Rate
0.0625 per unit time
Events / (Population × Time)
Odds
0.067
Risk / (1 − Risk)
How to Use This Calculator
- Enter the number of events (cases) observed.
- Provide the total population under observation.
- Optionally specify the time horizon to compute incidence rate.
- Review risk, rate, and odds to communicate event likelihoods.
Formula
Risk = Events / Population
Incidence Rate = Events / (Population × Time)
Odds = Risk / (1 − Risk)
Risk communicates probability over the observation period. Incidence rate normalizes by person-time, useful when follow-up durations differ. Odds are employed in logistic models and case-control studies.
Full Description
Risk metrics allow epidemiologists and actuaries to quantify event likelihoods. This tool translates raw counts into common measures, supporting decision-making for interventions, insurance pricing, or risk communication.
For small risks, odds approximate risk closely. As risk grows larger, odds diverge; always state which metric you are using to avoid misinterpretation.
Frequently Asked Questions
What if population changes over time?
Use person-time denominators (e.g., person-years) and enter that in the time horizon field to compute incidence rate.
Why is odds infinite?
If every individual experiences the event (risk = 1), the odds become infinite. This is rare outside of deterministic events.
How do I interpret incidence rate?
It expresses how quickly events occur per unit of person-time. Multiply by 1,000 or 100,000 to report standardized rates (e.g., per 100,000 person-years).
Can I compare two risks?
Use this calculator separately for each group, then compute risk ratios or differences. The relative risk calculator automates this comparison.