Free OnlineCalculators & Converters
Probability Calculator
Calculate probabilities for single events, compound events, Bayes' theorem, and binomial distributions. Essential for statistics and data science.
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Key Features — Probability Calculator
Single event probability
Compound events (AND, OR)
Independent and mutually exclusive events
Bayes' theorem posterior probability
Binomial distribution (exact + cumulative)
Why Use This Tool — Probability Calculator
Free Online Probability calculatorCalculate probability — for EveryoneFast & Easy Compound probability calculatorBayes theorem calculator — 100% FreeFree Online Binomial probability calculator
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Frequently Asked Questions — Probability Calculator
How do I calculate probability?
For a simple event: P = favorable outcomes / total outcomes. For example, rolling a 3 on a 6-sided die: P = 1/6 ≈ 0.167 or 16.7%. For compound events, you need to know whether the events are independent (one doesn't affect the other) or mutually exclusive (both can't happen at once).
What is Bayes' theorem?
Bayes' theorem calculates the probability of an event given prior knowledge. P(A|B) = P(B|A)·P(A) / P(B). Classic example: if a disease affects 1% of people and a test is 99% accurate with 5% false positive rate, a positive test result only means ~17% chance of actually having the disease — much lower than most people expect.
What is binomial probability?
Binomial probability calculates the chance of exactly k successes in n independent trials, each with probability p. P(X=k) = C(n,k) · p^k · (1-p)^(n-k). Example: probability of exactly 3 heads in 10 coin flips = C(10,3) · 0.5³ · 0.5⁷ ≈ 11.7%.