Bayes' Theorem Calculator

Calculate posterior probabilities using Bayes' Theorem with visual tree diagrams and step-by-step solutions.

Calculation Mode

Input Probabilities

P(A) - Prior Probability

Base probability that event A occurs

P(B|A) - Conditional Probability

Probability of B given A is true

P(B|A') - Conditional Probability if A is false

Probability of B given A is false

💡 Example: Rare Disease Test

• P(A) = 0.01 (disease affects 1% of population)

• P(B|A) = 0.95 (test is 95% accurate if you have disease)

• P(B|A') = 0.05 (5% false positive rate)

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Ready to Calculate

Enter your probabilities and click Calculate to see Bayes' Theorem in action

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Visualization Ready

Tree diagram will appear here after calculation