Statistics

Confidence Interval Calculator

A 95% confidence interval is a range built so that, if you repeated the sampling many times, 95% of those ranges would contain the true mean. Use t when the standard deviation comes from your sample, which is the usual case.

Your result will appear here.

How it's calculated

The standard error is the standard deviation divided by the square root of the sample size. Multiply it by the critical value for your confidence level to get the margin of error, then add and subtract that from the mean.

CI = x̄ ± critical value × s ÷ √n

How to do it in Excel

=CONFIDENCE.T(5%, 8.4, 40): Margin of error using t, for 95% confidence.
=CONFIDENCE.NORM(5%, 8.4, 40): Margin of error using z.