Confidence Interval Calculator

A confidence interval is a range that, under repeated sampling, would contain the true parameter a stated percentage of the time. Enter your data below.

How it works

For a mean, the tool uses the Student-t interval x̄ ± t*·(s/√n), with t* from the inverse Student-t at n−1 degrees of freedom. For a proportion, it defaults to the Wilson score interval (more accurate than the normal approximation, especially for small n or extreme p̂). All math runs client-side and is verified against NIST reference values — see Software & sources.