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Probability Calculator

Calculate event probabilities and combinations

Probability Calculator

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About This Calculator

A probability calculator helps you compute the likelihood of events and count possible arrangements. It covers single event probability (P = favorable outcomes / total outcomes), combinations (nCr — the number of ways to choose r items from n items where order does not matter), and permutations (nPr — the number of ways to arrange r items from n items where order matters). Enter favorable and total outcomes to find the probability of an event, or use the combinations and permutations modes to count possible selections and arrangements. This calculator is useful for students learning probability and statistics, data analysts working with likelihood models, quality control calculations, risk assessment, and anyone making decisions under uncertainty.

How to Use

  1. 1
    Select calculation type
    Choose from basic probability, combinations (nCr), or permutations (nPr).
  2. 2
    Enter your values
    Input the relevant numbers such as favorable and total outcomes.
  3. 3
    View the result
    See the probability expressed as a fraction, decimal, and percentage.

Frequently Asked Questions

Q. What is the difference between combinations and permutations?
Combinations (nCr) count the number of ways to choose r items from n items when order does not matter. Permutations (nPr) count the ways when order does matter. For example, choosing 3 people from 10 for a committee is a combination (C(10,3) = 120), but assigning them president/VP/secretary roles is a permutation (P(10,3) = 720).
Q. How is basic probability calculated?
Basic probability is calculated as the number of favorable outcomes divided by the total number of possible outcomes: P = favorable / total. For example, the probability of drawing a heart from a standard deck is 13/52 = 0.25 or 25%.
Q. How do I calculate the probability of at least one success?
Use the complement: P(at least one) = 1 − P(none). For example, the probability of rolling at least one 6 in four dice rolls is 1 − (5/6)^4 = 1 − 0.482 = 0.518 or about 51.8%. This approach is much simpler than adding up every individual success scenario.

Disclaimer: Results are for informational purposes only and do not constitute professional advice. Always consult qualified professionals for important decisions.

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