Statistics & Probability Calculators
Conditional Probability Calculator
Compute P(A | B) from P(A ∩ B) and P(B).
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What is Conditional Probability?
A conditional probability is the chance of A once B is known to have happened: P(A | B) = P(A ∩ B) ÷ P(B). Conditioning narrows the sample space to B, so the same event can look much more or much less likely than it did unconditionally.
How it works
The joint probability is divided by the probability of the condition. The page refuses to divide by zero and says why — if B never happens, P(A | B) is undefined rather than infinite — and it checks that the joint cannot exceed P(B), which a typo often violates.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.