About This Tool
The Probability Calculator finds the probability of single events, combined AND/OR events, and the probability of an event NOT occurring.
Frequently Asked Questions
How is probability calculated?
Probability = Number of Favourable Outcomes / Total Possible Outcomes, giving a value between 0 (impossible) and 1 (certain).
What is the probability of A AND B?
For independent events, P(A and B) = P(A) × P(B).
What is the probability of A OR B?
For mutually exclusive events, P(A or B) = P(A) + P(B). For non-exclusive events, P(A or B) = P(A) + P(B) - P(A and B).