Work out the odds. Find the probability of a single event from favorable and total outcomes, or combine two independent events with P(A and B) and P(A or B).
Example: rolling a 4 on a die = 1 out of 6.
Enter each as a probability between 0 and 1 (e.g. 0.5) — values you type as percents like 50 are read as 0.5 automatically.
Results update as you type. Probabilities are clamped to the valid 0–1 range.
Divide the number of favorable outcomes by the total number of possible outcomes. For example, rolling a 4 on a six-sided die is 1 favorable outcome out of 6, so the probability is 1 ÷ 6 = 0.1667, or about 16.67%.
Multiply their individual probabilities: P(A and B) = P(A) × P(B). For example, if P(A) is 0.5 and P(B) is 0.5, then P(A and B) = 0.5 × 0.5 = 0.25.
Add the two probabilities and subtract the chance of both: P(A or B) = P(A) + P(B) − P(A) × P(B). For P(A) = 0.5 and P(B) = 0.5 this gives 0.5 + 0.5 − 0.25 = 0.75.