This probability calculator converts favorable and total outcomes into a probability, percentage, and the complement chance.
Statistics
Probability Calculator
Compute event and complement probabilities from equally likely outcomes.
Calculator
About this calculator
Formula notes
P = favorable / total; complement P′ = 1 − P.
Worked examples
- Example: 1 favorable outcome out of 6 gives P = 1/6 ≈ 0.167, i.e. 16.67%, with an 83.3% complement.
- With 7 favourable outcomes among 40 equally likely outcomes, event probability is 7/40 = 17.5% and complement probability is 82.5%.
How to use it
- Enter the number of favorable outcomes.
- Enter the total number of equally likely outcomes.
- Read the probability, percentage, and complement.
Frequently asked questions
Does this assume equally likely outcomes?
Yes. The simple ratio only works when every outcome has the same chance, like fair dice.
What does the complement tell me?
It is the chance the event does not happen — useful for at-least-one style questions.
Limits and interpretation
- The favourable-over-total formula assumes outcomes are mutually exclusive, exhaustive, and equally likely.
- Dependent events, changing probabilities, continuous outcomes, and conditional information require a different model.