Probability Calculator
Work out basic probabilities from favorable and total outcomes, then combine two independent events using AND, OR, and NOT rules. Probability measures how likely something is on a scale from zero to one, and this calculator shows each answer three ways: as a reduced fraction, a decimal, and a percentage, so you can use whichever your assignment or bet slip expects. Enter the number of favorable outcomes and total outcomes for a single event to get its chance, then feed two event probabilities into the combination section to see the odds that both happen, that at least one happens, or that neither happens. It assumes the two events are independent, which is the most common textbook case. All of the math runs locally in your browser, so your numbers stay private and results are instant.
How to use Probability Calculator
- Enter the probability of each event.
- Choose whether you want AND, OR, or NOT.
- Read the result as a fraction, decimal and percentage.
Frequently asked questions
How does the AND rule work?
For independent events the probability of both happening is the product of their individual probabilities.
How does the OR rule work?
The probability of either event is the sum of the two probabilities minus the chance of both, which avoids double counting.
What does NOT return?
The probability of an event not happening is 1 minus the probability of it happening.
What is Probability Calculator?
Work out basic probabilities from favorable and total outcomes, then combine two independent events using AND, OR, and NOT rules. Probability measures how likely something is on a scale from zero to one, and this calculator shows each answer three ways: as a reduced fraction, a decimal, and a percentage, so you can use whichever your assignment or bet slip expects.
Is Probability Calculator free to use?
Yes. Probability Calculator is completely free, with no sign-up and no usage limits.
Does Probability Calculator work in a web browser?
Yes. Probability Calculator runs in any modern web browser. There is nothing to download or install.
Is my data private with Probability Calculator?
Yes. Probability Calculator runs entirely on your device in your browser, so nothing you enter is uploaded to a server.
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