EVERYDAY CLARITY
Conditional Probability Calculator
Calculate a conditional probability from joint event probability and the conditioning event probability.
Your result
Probability of A given B
Result for the values shown.
Calculations run in your browser.
What to enter
| Input | Meaning and units |
|---|---|
| Probability of A and B | Enter probability of a and b using the definition in the method and example. |
| Probability of B | Enter probability of b using the definition in the method and example. |
Understanding your result
These outputs describe the probability model and event definitions you entered. A probability is a number from 0 to 1; a probability density is not itself the probability of one exact continuous value.
Common mistakes
- Entering 25 instead of 0.25 for a probability, or assuming events are independent when the model requires that assumption.
- Confusing an exact-count probability with a cumulative probability, or replacement with sampling without replacement.
Check your calculation
- Check a zero/certain-event boundary and the stated support of the distribution against the worked example.
Calculation checks, sources and review limits
What is the probability of A when I already know B occurred?
Calculate a conditional probability from joint event probability and the conditioning event probability.
Common uses
- What is the probability of A when I already know B occurred
How it works
probability = joint / b
Worked example
Enter Probability of A and B: 0.12 ; Probability of B: 0.3 . Results: Probability of A given B: 0.4 .