Method
For the stated z-based method, interval = mean ± z_(1−α/2) × SD/√n. The margin equals critical value times standard error.
Math worksheet
Confidence Interval Calculator
Estimate a two-sided interval for a mean from a point estimate, standard deviation, sample size and chosen confidence level.
The calculation runs locally. Exact-integer tools avoid floating point; decimal and transcendental tools report rounding limits.
Method and verification guide
How the Confidence Interval Calculator works
For the stated z-based method, interval = mean ± z_(1−α/2) × SD/√n. The margin equals critical value times standard error. The calculator keeps the intermediate values visible so you can reproduce the answer independently.
Interpret the result
Under repeated sampling and the method assumptions, the stated proportion of constructed intervals captures the population mean.
Check the assumptions
This z interval assumes a known or adequately estimated population spread and independent representative observations; it does not remove bias.
Local calculation
Everything runs in this browser. Inputs are not sent to an external calculator.
Rounding
Displayed values may be rounded for readability while calculations use full floating-point precision unless the tool explicitly uses exact integers.
Scope
This z interval assumes a known or adequately estimated population spread and independent representative observations; it does not remove bias.
Simple by design
Three steps to a clearer number.
Enter your details
Use realistic values in each field. You can change them anytime.
Calculate instantly
The formula runs locally, so there is no account or waiting time.
Use the result
Treat the answer as a practical estimate for your next decision.