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Probability Calculator
Work out the probability of a single event or of two events combined, with the answer shown as a decimal, a percentage and odds.
Probability of an event
Probability: —
Percentage: — · Odds: —
How to use the Probability Calculator
- Choose the probability calculation you need from the list.
- Enter the outcomes or probabilities in the two boxes.
- Read the probability, the percentage and the odds in the result panel.
Features
- Single event probability from outcomes
- And, or, complement and conditional rules
- Answer shown as a decimal, a percentage and odds
- Runs locally, no uploads
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Frequently Asked Questions
Common questions about the free online probability calculator.
Choose the calculation, enter the outcomes or probabilities, and the answer appears as a
decimal, a percentage and odds.
Multiply the two probabilities together. Two events with probability 0.5 each give a combined
probability of 0.25.
Add the two probabilities and subtract their product: P(A) plus P(B) minus P(A) times P(B).
Two events are mutually exclusive when they cannot happen at the same time, so their
probabilities simply add.
It is the chance of one event given that another has happened, found by dividing the joint
probability by P(B).
The odds show how many attempts you would expect for one success, so a probability of 0.5
gives 1 in 2.
No. A probability always lies between 0 for an impossible event and 1 for an event that is
certain.
It is the chance that the event does not happen, which is 1 minus its probability.
No. All probability maths runs locally in your browser, so nothing is sent anywhere.
Yes. It is completely free and unlimited, with no account, no sign-up and no usage caps.
Last updated: October 10, 2026