Probability Calculator
Calculate common probabilities with live formulas, validation, visual interpretation, and research-friendly output.
Use counts when all outcomes are equally likely. Probability = favorable outcomes ÷ total outcomes.
The complement is the probability that event A does not occur: P(Aᶜ) = 1 − P(A).
For any two events: P(A ∪ B) = P(A) + P(B) − P(A ∩ B). The overlap cannot exceed either event.
For independent events, P(A ∩ B) = P(A) × P(B).
Conditional probability uses the overlap relative to event B: P(A | B) = P(A ∩ B) ÷ P(B), where P(B) > 0.
Binary Bayes model: update a prior P(A) after observing B using P(B|A) and P(B|Aᶜ).
For independent trials with constant success probability p, calculate at least one, none, all, and expected successes.
Convert probability p to odds in favor p:(1−p), odds against (1−p):p, and decimal odds 1/p.
Probability
0.300000
30.0000%
Complement
0.700000
Percentage
30.0000%
Odds in favor
0.428571 : 1
How this is calculated
The result is the share of equally likely outcomes that satisfy the event.
