Probability Calculator
Calculate simple-event probability from favorable and total outcomes, or compare two independent events. Results include decimal probability, percentage, complement, intersection, union and the probability that neither event occurs.
Simple probability
Two independent events
The two-event calculations assume that A and B are independent.
How to use the Probability Calculator
- For a simple event, enter the number of favorable outcomes and the total number of equally likely outcomes.
- Probability is favorable outcomes divided by total possible outcomes.
- The complement is one minus the event probability.
- For independent events, the probability that both occur is P(A) multiplied by P(B).
- The union of two independent events is P(A) + P(B) − P(A and B).
Examples
Rolling a six
One favorable face out of six equally likely die faces gives probability 1/6, or about 16.67%.
Coin toss
A fair coin has probability 0.5 for heads and 0.5 for tails.
Two independent events
If P(A)=0.5 and P(B)=0.5, the probability both occur is 0.25.
Frequently asked questions
Can probability be greater than 1?
No. A probability ranges from 0 for impossible to 1 for certain.
How do I convert probability to a percentage?
Multiply the decimal probability by 100.
What is a complement?
The complement is the probability that an event does not happen and equals 1 minus the event probability.
What does independent events mean?
Events are independent when the occurrence of one does not change the probability of the other.
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