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Confidence Interval Calculator

Build confidence intervals for means, proportions, and differences between groups at 80%, 90%, 95%, or 99% confidence levels.

Confidence interval for a single mean using z* s / sqrt(n).

Confidence level

Critical value method

Sample mean (x-bar)

Sample standard deviation (s)

Sample size (n)

confidence interval calculator95% confidence interval for mean or proportion

Critical value (z* / t*)

1.96

Degrees of freedom (t)

Point estimate

Margin of error

0.715691

Confidence interval

(9.284309, 10.715691)

Choose the type of confidence interval you want to build (mean, proportion, or difference).
Enter the relevant sample statistics and select a confidence level such as 95%.
Read off the point estimate, margin of error, and the lower and upper bounds.

Quickly check 95% confidence intervals for means and proportions against your working.
Experiment with different confidence levels to see how the margin of error changes.
Use the difference in means or proportions to compare two groups with a single interval.

Uses z critical values by default, with optional t critical values for small-sample mean intervals.
Assumes reasonably large samples or approximate normality so normal and t approximations are valid.
Intervals are two-sided and symmetric around the point estimate.

Does this use z or t for the confidence interval?: You can choose. For large samples, use z. For small samples when estimating a mean, switch to t and the calculator will use an approximate t critical value based on the degrees of freedom.
Can I enter percentages instead of proportions?: Enter proportions as decimals between 0 and 1 (for example, 0.4 instead of 40%). This keeps the formulas consistent and reduces confusion.
What does a 95% confidence interval mean in plain language?: Roughly speaking, if you repeated the sampling process many times, about 95% of the constructed intervals would contain the true parameter.

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