Confidence Interval Calculator
Build a confidence interval for a sample proportion or for a mean when the population standard deviation is known.
Runs 100% in your browser — nothing is uploaded.
Estimate
%
Runs 100% in your browser — nothing is uploaded.
Result
Sample proportion
50%
Critical z*
1.96
Margin of error
3.1%
Confidence interval
[46.9%, 53.1%]
Formula
CI = estimate ± z* · standard error
About this calculator
A 95% confidence interval means that if you repeated the sampling process many times, about 95% of the intervals would contain the true value.
How to use
- 1
Choose proportion or mean.
- 2
Enter sample data and confidence level.
- 3
Read the interval and margin of error.
Frequently asked questions
What does 95% confidence actually mean?
It describes the method: 95% of intervals built this way from random samples will capture the true parameter. It is not the probability that this specific interval contains it.
Please note: Results are estimates for general information only and are not professional or medical/financial advice.