What This Calculator Does

This probability calculator brings together four common task types: permutations, combinations, binomial probabilities, and Poisson probabilities. You can think of it as a quick workbench for counting problems and discrete probability problems rather than as a page tied to just one formula.

It is especially useful in two situations. First, for learning and practice, when you want to check whether your final number looks right. Second, for light practical work, when you already know the model type and want to confirm the scale, expectation, or spread quickly without switching tools.

When to Use It

• You want a permutation or combination count.
• You want the probability of exactly k successes in a binomial setup.
• You want the probability of exactly k events in a Poisson setup.
• You want expectation, variance, and standard deviation alongside the headline result.
• You want a quick numerical check before writing the formal solution.

Inputs Explained

Mode

This calculator supports four modes:

• permutation
• combination
• binomial
• poisson

The most important choice is deciding whether your problem is about counting possibilities or about the probability of an outcome. Once that is clear, the page becomes much easier to use correctly.