Quick guide
How to use this calculator
- Enter the observations, probabilities, model parameters, or summary statistics requested by the visible labels.
- Keep every value on the same scale and confirm that the selected sampling relationship, distribution, and tail convention match the question you are investigating.
- Read the result together with its assumptions and interpretation. Statistical output summarizes uncertainty under a model; it does not repair biased data or establish causation.
Calculation method
How the repeated event probability calculator works
P(at least once)=1−(1−p)^n; minimum n=ceil[ln(1−target)/ln(1−p)].
More trials increase the chance of at least one event but do not guarantee when it occurs or make dependent trials independent.
Worked example
Repeated Event Probability example
With p=0.2 over 5 independent trials, the probability of at least one occurrence is 1−0.8⁵=0.67232.
P(at least once)=1−(1−p)^n; minimum n=ceil[ln(1−target)/ln(1−p)].
Supported inputs
Precision and limits
Model and design
Every trial must be independent with the same event probability; target is used only for the reverse at-least-once calculation.
Numerical scope
Inputs use double-precision numerical methods with guarded domains. Datasets accept up to 10,000 finite plain-decimal values. Extremely large parameters or probabilities deep in a numerical tail may require specialist statistical software.
Interpretation
More trials increase the chance of at least one event but do not guarantee when it occurs or make dependent trials independent.
Decision boundary
The calculator does not validate how data were collected, diagnose dependence or bias, choose a scientifically meaningful effect, or replace review by a qualified statistician for consequential research, medical, regulatory, safety, or policy decisions.
Privacy
Entered values and calculated results stay in this browser and are not sent to an analytics service.
Continue calculating