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Probability Calculator — Events & Binomial

Single events, independent AND/OR, and the binomial distribution P(X=k)/P(X≤k)/P(X≥k). Client-side.

Free No signup Client-side Privacy friendly Updated

Single event

Two independent events

Binomial — P(X = k)

How to use

  1. 1 Single event: favorable outcomes ÷ total outcomes.
  2. 2 Two independent events: enter each probability for AND / OR.
  3. 3 Binomial: n trials, k successes, success probability p.

Why use this tool

  • Three common probability problems in one place.
  • Includes the binomial distribution P(X = k), P(X ≤ k) and P(X ≥ k).
  • Runs entirely in your browser.

Frequently asked questions

How do I find a basic probability?

Divide the number of favorable outcomes by the total number of equally-likely outcomes.

What does “independent events” mean?

The outcome of one doesn’t affect the other. Then P(A and B) = P(A)·P(B), and P(A or B) = P(A) + P(B) − P(A)·P(B).

What is the binomial distribution?

The probability of exactly k successes in n independent trials each with success probability p: P(X = k) = C(n, k) pᵏ (1−p)ⁿ⁻ᵏ.

What are odds vs probability?

Probability is favorable ÷ total; odds are favorable : unfavorable. A probability of 1/4 is odds of 1 : 3.

What is Probability Calculator?

A probability calculator finds the probability of single and combined independent events (AND/OR) and the binomial distribution — the chance of k successes in n trials.

Features

Single, combined & binomial

Event probability with complement and odds; AND/OR of two events; and binomial P(X ≤ k).

Odds & complement

Shows the probability, its percentage, the complement (1 − p), and odds form.

Free & private

Runs on your device — nothing is uploaded.

Example

Input

favorable = 1, total = 6 (roll a specific die face)

Output

P = 0.1667 (16.67%) · complement = 0.8333 · odds = 1 : 5

Common use cases

  1. 1

    Games & gambling odds

    Work out the chance of an outcome and its odds.

  2. 2

    Combine events

    Find the probability that both, or either, of two independent events occur.

  3. 3

    Binomial trials

    Compute the chance of k successes in n independent trials.

Summary

Zerethon's probability calculator handles single-event probability (favorable ÷ total, with complement and odds), combined probability of two independent events (AND / OR), and the binomial distribution, all in your browser. Everything runs client-side — nothing is uploaded.

Category
Math
Pricing
Free
Privacy
Browser-based
Signup
Not required

References

Privacy

Your data never leaves your browser unless explicitly stated. Probability Calculator runs entirely client-side — no server upload, no logging, no tracking of your input.

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Mean vs Median Permutation vs Combination

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