How to use the Probability Calculator
This tool shows probabilities of two independent events happening together or separately.
Open the Probability Calculator →
What you need to enter
- P(A) (0–1)
- P(B) (0–1)
The formula
P(A and B) = P(A) × P(B). P(A or B) = P(A) + P(B) − P(A and B).
Worked example
Using the default values in the calculator:
- P(A) (0–1): 0.4
- P(B) (0–1): 0.3
| P(A and B) | 0.12 |
| P(A or B) | 0.58 |
| P(neither) | 0.42 |
| P(A only) | 0.28 |
| P(not A) | 0.6 |
| P(not B) | 0.7 |
Tips for better results
- Check that events are truly independent.
- Probabilities are between 0 and 1.
Common mistakes to avoid
- Entering percentages.
- Using it for dependent events.