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Wilson Confidence Interval for a Proportion Calculator

Wilson score interval — well-behaved when p is near 0 or 1.

Compute a Wilson score confidence interval for a single binomial proportion (95 % default). Outperforms the Wald interval at the boundaries (p ≈ 0 or 1) and for small samples.

Daniel Oh By Daniel Oh
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Wilson centre = (p̂ + z²/2n) / (1 + z²/n); half-width similar; bounds within [0,1].

In depth

Compute a Wilson score confidence interval for a single binomial proportion (95 % default). Outperforms the Wald interval at the boundaries (p ≈ 0 or 1) and for small samples.