What joint probability measures
Joint probability is the chance that two events both happen. Written P(A and B), it depends on whether the two events are independent (one has no effect on the other) or dependent (the outcome of one changes the odds of the other).
How this calculator works
For independent events, the calculator multiplies P(A) × P(B) directly. If you select dependent events, enter the conditional probability P(B|A) in the second field, and the calculator applies the general multiplication rule P(A and B) = P(A) × P(B|A). It also reports P(A or B) using the addition rule, which subtracts the overlap so it is not double-counted.
Joint probability calculations are used throughout statistics, risk analysis, and everyday decision-making. This tool is intended for general education and planning purposes.