Statistics & Probability

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Conditional Probability Calculator.

Calculate P(A given B) from a joint probability and P(B).

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01

Set your values

Results update as you type.

Conditional probability: 0.4

Conditional probability

0.400000
Percent: 40

Percent

40.000000

Results update automatically as you type.

Use Cases

Academic Statistics Practice

Students and teachers can quickly verify conditional probability calculations for homework or exam preparation, ensuring accuracy in understanding the relationship between events.

Example: Check P(A|B) when P(A∩B)=0.2 and P(B)=0.5.

Frequently Asked Questions

What is conditional probability?
Conditional probability measures the likelihood of event A occurring given that event B has already occurred. It is calculated as P(A|B) = P(A∩B) / P(B), where P(A∩B) is the probability of both events happening and P(B) is the probability of event B.
How do I use this calculator?
Simply enter the probability of both events occurring (P(A∩B)) and the probability of event B (P(B)) into the respective fields. The calculator instantly computes P(A|B) using the formula, with results updating as you type.
What if P(B) is zero?
If P(B) is zero, the conditional probability is undefined because you cannot condition on an impossible event. The calculator will not provide a valid result in that case, so ensure P(B) is greater than zero.

Tips & Common Mistakes

Tips

  • Ensure both probabilities are between 0 and 1, as probabilities outside this range are invalid.
  • Double-check that P(B) is not zero; otherwise, the conditional probability is undefined.
  • Use the debounced results to see updates as you type, making it easy to explore different scenarios.
  • Remember that P(A∩B) must be less than or equal to P(B) for a valid conditional probability.

Common Mistakes to Avoid

  • Entering percentages (e.g., 50%) instead of decimals (0.5) – always use decimal form.
  • Confusing P(A∩B) with P(A) – the calculator requires the joint probability, not the individual probability of A.
  • Forgetting that P(B) must be greater than zero; otherwise, the result is undefined.

Last updated: August 13, 2026