Math & Science
Confidence Interval Calculator
Calculate confidence intervals for means and proportions
Formulas and edge cases are reviewed against authoritative references before publication. For methodology, editorial standards, or corrections, use the links below.
Frequently asked questions
What does 95% confidence mean?
If we repeated the study 100 times, ~95 of those intervals would contain the true value.
Z or t distribution?
Use t for small samples (n<30) or unknown population standard deviation.
How to narrow the interval?
Increase sample size or accept lower confidence level.
Related tools
About this tool
This Confidence Interval Calculator turns your inputs into practical results. Provide Sample Mean, Standard Deviation, and Sample Size to calculate Lower Bound and Upper Bound.
Adjust values to compare scenarios and see how sensitive the result is. The calculation uses the numbers as entered, so double-check units and expect small differences from rounding in the displayed totals.