Toolstia / probability calculator
Probability calculator
Answer common probability questions: the chance of exactly or at least a number of successes, the chance of at least one success in a number of tries, and the odds of two independent events happening together.
Every try must have the same chance and not affect the others, like coin flips or dice rolls. Enter a percentage as a decimal, so 25% is 0.25.
How it works
- Choose what to work out.
- Enter the probabilities and number of tries.
- Read the results as percentages.
Binomial probability
If every try has the same chance of success p, the chance of exactly k successes in n tries follows the binomial distribution. The tool also gives the chance of k or fewer, k or more, and the expected number of successes.
At least one
The chance of at least one success in n tries is 1 minus the chance of none: 1 minus (1 minus p) raised to n. Rolling a six in six rolls has a chance of about 66.5 percent.
Two independent events
For events that do not affect each other, the chance of both is the two probabilities multiplied. The chance of at least one is A plus B minus both.
Enter decimals
Probabilities go in as decimals from 0 to 1, so 25 percent is 0.25.
Questions
What does independent mean?
The result of one event does not change the chance of the other, like two separate coin flips.
What is the limit for n?
The binomial mode supports up to 5,000 tries.
Is my data stored?
Everything happens in your browser, and nothing you type is sent anywhere.