Quick start
- Choose Mean interval or Proportion interval.
- Choose a confidence level.
- Enter the sample values requested by that mode.
- Press Calculate interval and review the bounds and formula steps.
Mean intervals
Mean mode uses the sample mean, standard deviation, and sample size to estimate a range around the mean.
The calculator shows the standard error and z critical value used in the margin of error.
Proportion intervals
Proportion mode uses successes divided by sample size as the point estimate.
The interval is clipped to stay within 0% and 100% because proportions cannot fall outside that range.
Examples from the calculator
67.02 to 68.98
42.2% to 61.8%
67.1775 to 68.8225
History, privacy, and copying
Recent answers stay visible in the page while you work. The history is kept only in the current browser tab and is not sent to a server.
Copy answer copies the expression and result so you can paste it into notes, homework, a message, or another document.