Confidence Interval Calculator

What a Confidence Interval Tells You

Rather than reporting a single sample mean as if it were the exact population mean, a confidence interval gives a range that is likely to contain the true population mean, along with a stated confidence level (like 95%) describing how often intervals built this way would capture the true value across repeated sampling.

x̄ = sample mean, z = z-score for the confidence level, σ = standard deviation, n = sample size

Choosing a Confidence Level

A higher confidence level (like 99% instead of 90%) produces a wider interval, because being more certain the true mean is captured requires allowing for a larger margin of error.