Probability Calculator
Calculate probability of events — single events, multiple events (AND/OR), complements, and conditional probability.
Inputs
Results
Probability Rules
P(A AND B) = P(A) × P(B) for independent events. P(A OR B) = P(A) + P(B) − P(A AND B). P(A|B) = P(A AND B) / P(B) (conditional probability). All probabilities are between 0 (impossible) and 1 (certain). P(A') = 1 − P(A) (complement).
What is the Probability Calculator?
The Probability Calculator assesses the likelihood of a specific event occurring. It can analyze both single events (like rolling a die) and complex compound events (like drawing two specific cards in a row from a deck).
How It Works (Formula)
Basic probability is the number of desired outcomes divided by the total number of possible outcomes. For compound events, the calculator uses the multiplication rule. If events are independent, $P(A \text{ and } B) = P(A) \times P(B)$.
$$ P(\text{Event}) = \frac{\text{Number of Favorable Outcomes}}{\text{Total Number of Possible Outcomes}} $$
The fundamental formula of statistical probability.
How to Use It
Define your scenario. Enter the probability of Event A occurring, and the probability of Event B occurring. The calculator will reveal the exact odds of both occurring, either occurring, or neither occurring.