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Proportion Margin of Error Calculator

Estimate normal-approximation margin of error for a proportion.

Data stays on this deviceConvention explained below

Data and assumptions

Runs on your device

STATISTICAL RESULT

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter observed proportion, sample size, critical z value.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

Margin = z√[p(1 − p)/n], expressed in percentage points.

A WORKED EXAMPLE

Using observed proportion = 0.5, sample size = 400, critical z value = 1.95996398454, the result is 4.89990996 percentage points. Change these example inputs to match your task; use the method above to check each step.

What to keep in mind

Normal approximation may be unreliable for small counts or proportions near zero or one. A descriptive or probability calculation under the stated assumptions. Check the sample design and model before interpreting results.

Common questions

Which inputs does this calculation need?

Estimate normal-approximation margin of error for a proportion. Enter observed proportion, sample size, critical z value. The filled example is editable and is not a saved personal record.

How should I interpret the result?

Normal approximation may be unreliable for small counts or proportions near zero or one. A descriptive or probability calculation under the stated assumptions. Check the sample design and model before interpreting results.

Methodology maintained by ClarityKit. How these tools are built and checked.