Probability Calculator

Divide the number of favorable outcomes by the total number of possible outcomes. For example, rolling a 4 on a six-sided die has 1 favorable outcome out of 6 possible, so the probability is 1 ÷ 6 ≈ 0.167, or 16.7%.

For two independent events, multiply their probabilities: P(A and B) = P(A) × P(B). For example, flipping two heads in a row is 0.5 × 0.5 = 0.25, or 25%. This calculator assumes the two events are independent — one does not affect the other.

Use P(A or B) = P(A) + P(B) − P(A and B). Subtracting the overlap prevents double-counting the cases where both occur. For mutually exclusive events (that can not both happen), the overlap is zero, so you simply add the two probabilities.

Independent events do not influence each other — the outcome of one says nothing about the other (like two separate coin flips). Mutually exclusive events cannot both happen at once (like a single coin landing both heads and tails). This tool computes the "and"/"or" values assuming independence.

P(not A) is the complement — the probability that event A does not happen. Since something either happens or it does not, P(not A) = 1 − P(A). If there is a 30% chance of rain, there is a 70% chance of no rain.