Binomial probability calculator

Calculate exact-count probability with your own figures.

Your numbers

Use the units shown. Results update as you change valid inputs.

Use exact-count probability to compare changes to your inputs. The method and limits below explain the scope.

Examples

Examples

Try the starting example

Trials
10
Success probability
0.5
Successes
5
Exact-count probability
0.246094

Try another scenario

Trials
11
Success probability
0.5
Successes
5
Exact-count probability
0.225586
Calculation method

Calculation method

Exact-count probability

(combinations(a,c)) × b^c × (1-b)^(a-c)

Symbols and units
a
Trials
b
Success probability
c
Successes

Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.

Calculation steps and notation

combinations(n, k) = n! / (k! × (n−k)!), counting unordered selections without replacement. The implementation uses exact integer products and divisions, with n at most 500.

Assumptions & limits

Assumptions & limits

  • Independent Bernoulli trials with the same probability.
Are these inputs private?

These calculations run in your browser. A shared link contains the values you choose to share. Only questions submitted to the separate AI finder are sent to OpenAI.

Further reading

Method reference ↗

Background reading; this does not imply endorsement or independent review of SumFizz.

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