Probability Calculator
Calculate P(event) from favorable and total outcomes.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Enter the number of favorable outcomes and the total number of possible outcomes. The calculator divides favorable by total to give you the probability as a decimal, percentage, and odds format. It also shows the complement (probability the event does not happen).
About Probability
Probability measures the likelihood of an event occurring, expressed as a number between 0 (impossible) and 1 (certain). The basic formula is P(A) = favorable outcomes / total outcomes. This applies to equally likely outcomes. For complex scenarios involving multiple events, you may need conditional probability, Bayes' theorem, or combinatorics.
Frequently Asked Questions
What is the difference between probability and odds?
Probability is favorable / total (e.g., 1/6). Odds compare favorable to unfavorable (e.g., 1:5). They convey the same information in different formats.
What is a complement in probability?
The complement P(A') = 1 - P(A). It is the probability the event does NOT happen. Useful when it is easier to calculate what will not happen.
Can probability be greater than 1?
No. Probability is always between 0 and 1 inclusive. If favorable outcomes exceed total outcomes, the input is invalid.