Probability Calculator
Calculate probability of events including single, multiple, conditional, and Bayesian probability.
Result
Fill in the fields above, then press Calculate.
A probability calculator computes the likelihood of events using basic probability rules, combinations, and permutations.
Examples
Coin and Die
P(heads AND rolling 6) = 0.5 × (1/6) = 0.0833 or 8.33%
Drawing cards
P(red OR face card) = 26/52 + 12/52 - 6/52 = 32/52 = 0.615
Conditional
If P(rain|cloudy) = 0.4 and P(cloudy) = 0.3, then P(rain AND cloudy) = 0.12
Frequently Asked Questions
What is the difference between P(A ∩ B) and P(A ∪ B)?
P(A ∩ B) is the probability both events occur (AND). P(A ∪ B) is the probability at least one event occurs (OR).
What does conditional probability mean?
P(A|B) is the probability of event A occurring given that event B has already occurred.
When are events independent?
Events are independent when the occurrence of one does not affect the probability of the other, meaning P(A|B) = P(A).
Result
Your result appears here and follows you as you scroll.
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Quick Tips
- •Double-check your inputs — small errors lead to incorrect results.
- •Use decimal form for fractions when entering probability values (e.g., 0.5 instead of 1/2).
- •Remember that P(A or B) must account for overlap by subtracting P(A and B).