Statistics & Probability Calculators
Confidence Interval Calculator
Build a confidence interval for a mean, using the t value for small samples.
Loading tool…
What is Confidence Interval?
A confidence interval is a range that is expected to contain the true mean at a stated confidence: x̄ ± critical × (s ÷ √n). The critical value comes from the t distribution for small samples and the normal distribution for large ones.
How it works
The tool picks t while the degrees of freedom are 30 or fewer and z after that — the conventional threshold, which the page states rather than hides — and the interval, its margin of error and the critical value are all shown so the result can be reconstructed by hand.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.