Math
Probability Calculator
P(A and B), P(A or B), and conditional probability for any two events.
Independent events (assumed here)
These calculations assume A and B are independent — one doesn't affect the other. If events are dependent, conditional probability applies: P(A|B) = P(A and B) / P(B).
The rules
P(A and B) = P(A) × P(B) [independent]
P(A or B) = P(A) + P(B) − P(A and B)
P(not A) = 1 − P(A)
Real-world example
60% chance of rain, 40% chance of traffic: P(rain AND traffic) = 0.6 × 0.4 = 24%. P(at least one problem) = 0.6 + 0.4 − 0.24 = 76%.
⚡ CalcWolf Insight
The birthday paradox: in a group of just 23 people, there is a 50% chance that two people share the same birthday.
Frequently asked questions
What is the probability of two independent events both occurring?▾
Multiply their individual probabilities. P(A) = 60%, P(B) = 40%: P(both) = 0.60 × 0.40 = 0.24 = 24%.
What is the difference between probability and odds?▾
Probability is the chance of an event occurring out of all possible outcomes (e.g., 1/6 for rolling a specific die number). Odds compare favorable to unfavorable outcomes (e.g., 1:5 against). A 25% probability equals 1:3 odds. Gambling uses odds; science uses probability.
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