Probability Calculator
Calculate single-event, combined, and complementary probabilities.
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Common probability calculations
This probability calculator helps estimate single events, complements, intersections, and union probabilities. It is useful for raffles, dice, coin flips, game design, risk checks, and basic statistics practice.
Before using a probability formula, decide whether the events are independent, mutually exclusive, or overlapping. The correct formula depends on that relationship.
Formula or logic
- Complement: P(not A) = 1 - P(A)
- Independent intersection: P(A and B) = P(A) × P(B)
- At least one event: P(A or B) = P(A) + P(B) - P(A and B)
Example
If the chance of winning is 10%, the chance of not winning is 90%. If two independent draws each have a 10% win chance, the chance of winning both is 1%.
Common questions
What is an independent event?
Two events are independent when the result of one does not change the probability of the other.
Can mutually exclusive events happen together?
No. Mutually exclusive events cannot happen at the same time in a single trial.
Can probability be above 100%?
No. A valid probability must stay between 0% and 100%, or between 0 and 1.