Confidence Interval Calculator

Calculate a confidence interval for a sample mean or a sample proportion, using the standard z-score method.

Sample data

Estimate type

Confidence level (%)

Sample mean

Sample standard deviation

Sample size (n)

Notes

This calculator uses the normal (z-score) approximation, which is standard practice for sample sizes of 30 or more. For small samples with an unknown population standard deviation, a t-distribution gives a wider, more accurate interval.