Probability Calculator
Calculate event probability from favorable and total outcomes, then optionally combine two independent events.
Probability of A0%
Probability of NOT A0%
Probability of B—
A AND B (independent)—
A OR B (independent)—
How to Use the Probability Calculator
Enter the number of favorable outcomes and total possible outcomes, or use the available probability inputs, to calculate an event probability.
Practical Example
If 3 outcomes are favorable out of 10 equally likely outcomes, the probability is 3 divided by 10, or 30%.
Factors That Affect the Result
Probability calculations depend on correctly defining the event, the sample space and whether outcomes are equally likely or independent.
Frequently Asked Questions
Can probability exceed 100%?
No. A valid probability ranges from 0% to 100%.
What does a probability of 0 mean?
It means the event is impossible under the stated assumptions.
What does a probability of 1 mean?
It means the event is certain under the stated assumptions.