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Statistics

Bayes’ Theorem Calculator

Update a prior probability using two conditional likelihoods.

Data stays on this deviceConvention explained below

Data and assumptions

Runs on your device

STATISTICAL RESULT

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter prior probability of a, probability of b given a, probability of b given not a.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

P(A given B) = prior × likelihood/[prior × likelihood + (1 − prior) × other likelihood].

A WORKED EXAMPLE

Using prior probability of a = 0.1, probability of b given a = 0.8, probability of b given not a = 0.2, the result is 0.307692308 probability. Change these example inputs to match your task; use the method above to check each step.

What to keep in mind

Generic probability model; this tool does not interpret medical test results. A descriptive or probability calculation under the stated assumptions. Check the sample design and model before interpreting results.

Common questions

Which inputs does this calculation need?

Update a prior probability using two conditional likelihoods. Enter prior probability of a, probability of b given a, probability of b given not a. The filled example is editable and is not a saved personal record.

How should I interpret the result?

Generic probability model; this tool does not interpret medical test results. A descriptive or probability calculation under the stated assumptions. Check the sample design and model before interpreting results.

Methodology maintained by ClarityKit. How these tools are built and checked.