Probability Calculator — Events & Binomial
Single events, independent AND/OR, and the binomial distribution P(X=k)/P(X≤k)/P(X≥k). Client-side.
Single event
Two independent events
Binomial — P(X = k)
How to use
- 1 Single event: favorable outcomes ÷ total outcomes.
- 2 Two independent events: enter each probability for AND / OR.
- 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 : 5Common use cases
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1
Games & gambling odds
Work out the chance of an outcome and its odds.
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2
Combine events
Find the probability that both, or either, of two independent events occur.
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3
Binomial trials
Compute the chance of k successes in n independent trials.
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
- Probability — Wolfram MathWorld — Wolfram MathWorld
- Probability — Wikipedia
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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